diff --git a/server/channelserver/handlers_session.go b/server/channelserver/handlers_session.go
index 75eaac40e..80bf3de4f 100644
--- a/server/channelserver/handlers_session.go
+++ b/server/channelserver/handlers_session.go
@@ -292,11 +292,20 @@ func logoutPlayer(s *Session) {
 	_ = s.rawConn.Close()
 	s.server.Unlock()
 
-	// Stage cleanup
+	// Stage cleanup — snapshot sessions first under server mutex, then iterate stages under stagesLock
+	s.server.Lock()
+	sessionSnapshot := make([]*Session, 0, len(s.server.sessions))
+	for _, sess := range s.server.sessions {
+		sessionSnapshot = append(sessionSnapshot, sess)
+	}
+	s.server.Unlock()
+
+	s.server.stagesLock.RLock()
 	for _, stage := range s.server.stages {
-		// Tell sessions registered to disconnecting players quest to unregister
+		stage.Lock()
+		// Tell sessions registered to disconnecting player's quest to unregister
 		if stage.host != nil && stage.host.charID == s.charID {
-			for _, sess := range s.server.sessions {
+			for _, sess := range sessionSnapshot {
 				for rSlot := range stage.reservedClientSlots {
 					if sess.charID == rSlot && sess.stage != nil && sess.stage.id[3:5] != "Qs" {
 						sess.QueueSendMHFNonBlocking(&mhfpacket.MsgSysStageDestruct{})
@@ -309,7 +318,9 @@ func logoutPlayer(s *Session) {
 				delete(stage.clients, session)
 			}
 		}
+		stage.Unlock()
 	}
+	s.server.stagesLock.RUnlock()
 
 	// Update sign sessions and server player count
 	if s.server.db != nil {
@@ -339,11 +350,13 @@ func logoutPlayer(s *Session) {
 		CharID: s.charID,
 	}, s)
 
-	s.server.Lock()
+	s.server.stagesLock.RLock()
 	for _, stage := range s.server.stages {
+		stage.Lock()
 		delete(stage.reservedClientSlots, s.charID)
+		stage.Unlock()
 	}
-	s.server.Unlock()
+	s.server.stagesLock.RUnlock()
 
 	removeSessionFromSemaphore(s)
 	removeSessionFromStage(s)
diff --git a/server/channelserver/handlers_stage.go b/server/channelserver/handlers_stage.go
index 698c85940..65b7ce790 100644
--- a/server/channelserver/handlers_stage.go
+++ b/server/channelserver/handlers_stage.go
@@ -14,8 +14,8 @@ import (
 
 func handleMsgSysCreateStage(s *Session, p mhfpacket.MHFPacket) {
 	pkt := p.(*mhfpacket.MsgSysCreateStage)
-	s.server.Lock()
-	defer s.server.Unlock()
+	s.server.stagesLock.Lock()
+	defer s.server.stagesLock.Unlock()
 	if _, exists := s.server.stages[pkt.StageID]; exists {
 		doAckSimpleFail(s, pkt.AckHandle, []byte{0x00, 0x00, 0x00, 0x00})
 	} else {
@@ -30,24 +30,20 @@ func handleMsgSysCreateStage(s *Session, p mhfpacket.MHFPacket) {
 func handleMsgSysStageDestruct(s *Session, p mhfpacket.MHFPacket) {}
 
 func doStageTransfer(s *Session, ackHandle uint32, stageID string) {
-	s.server.Lock()
+	s.server.stagesLock.Lock()
 	stage, exists := s.server.stages[stageID]
-	s.server.Unlock()
-
-	if exists {
-		stage.Lock()
-		stage.clients[s] = s.charID
-		stage.Unlock()
-	} else { // Create new stage object
-		s.server.Lock()
+	if !exists {
 		s.server.stages[stageID] = NewStage(stageID)
 		stage = s.server.stages[stageID]
-		s.server.Unlock()
-		stage.Lock()
-		stage.host = s
-		stage.clients[s] = s.charID
-		stage.Unlock()
 	}
+	s.server.stagesLock.Unlock()
+
+	stage.Lock()
+	if !exists {
+		stage.host = s
+	}
+	stage.clients[s] = s.charID
+	stage.Unlock()
 
 	// Ensure this session no longer belongs to reservations.
 	if s.stage != nil {
@@ -55,8 +51,11 @@ func doStageTransfer(s *Session, ackHandle uint32, stageID string) {
 	}
 
 	// Save our new stage ID and pointer to the new stage itself.
+	s.server.stagesLock.RLock()
+	newStage := s.server.stages[stageID]
+	s.server.stagesLock.RUnlock()
 	s.Lock()
-	s.stage = s.server.stages[stageID]
+	s.stage = newStage
 	s.Unlock()
 
 	// Tell the client to cleanup its current stage objects.
@@ -141,8 +140,8 @@ func doStageTransfer(s *Session, ackHandle uint32, stageID string) {
 }
 
 func destructEmptyStages(s *Session) {
-	s.server.Lock()
-	defer s.server.Unlock()
+	s.server.stagesLock.Lock()
+	defer s.server.stagesLock.Unlock()
 	for _, stage := range s.server.stages {
 		// Destroy empty Quest/My series/Guild stages.
 		if stage.id[3:5] == "Qs" || stage.id[3:5] == "Ms" || stage.id[3:5] == "Gs" || stage.id[3:5] == "Ls" {
@@ -195,9 +194,9 @@ func removeSessionFromStage(s *Session) {
 }
 
 func isStageFull(s *Session, StageID string) bool {
-	s.server.Lock()
+	s.server.stagesLock.RLock()
 	stage, exists := s.server.stages[StageID]
-	s.server.Unlock()
+	s.server.stagesLock.RUnlock()
 
 	if exists {
 		// Lock stage to safely check client counts
@@ -256,9 +255,20 @@ func handleMsgSysBackStage(s *Session, p mhfpacket.MHFPacket) {
 		return
 	}
 
-	delete(s.stage.reservedClientSlots, s.charID)
+	if s.stage != nil {
+		s.stage.Lock()
+		delete(s.stage.reservedClientSlots, s.charID)
+		s.stage.Unlock()
+	}
 
-	delete(s.server.stages[backStage].reservedClientSlots, s.charID)
+	s.server.stagesLock.RLock()
+	backStagePtr, exists := s.server.stages[backStage]
+	s.server.stagesLock.RUnlock()
+	if exists {
+		backStagePtr.Lock()
+		delete(backStagePtr.reservedClientSlots, s.charID)
+		backStagePtr.Unlock()
+	}
 
 	doStageTransfer(s, pkt.AckHandle, backStage)
 }
@@ -278,7 +288,10 @@ func handleMsgSysLeaveStage(s *Session, p mhfpacket.MHFPacket) {}
 
 func handleMsgSysLockStage(s *Session, p mhfpacket.MHFPacket) {
 	pkt := p.(*mhfpacket.MsgSysLockStage)
-	if stage, exists := s.server.stages[pkt.StageID]; exists {
+	s.server.stagesLock.RLock()
+	stage, exists := s.server.stages[pkt.StageID]
+	s.server.stagesLock.RUnlock()
+	if exists {
 		stage.Lock()
 		stage.locked = true
 		stage.Unlock()
@@ -288,17 +301,26 @@ func handleMsgSysLockStage(s *Session, p mhfpacket.MHFPacket) {
 
 func handleMsgSysUnlockStage(s *Session, p mhfpacket.MHFPacket) {
 	if s.reservationStage != nil {
+		// Read reserved client slots under stage RLock
 		s.reservationStage.RLock()
-		defer s.reservationStage.RUnlock()
-
+		var charIDs []uint32
 		for charID := range s.reservationStage.reservedClientSlots {
+			charIDs = append(charIDs, charID)
+		}
+		stageID := s.reservationStage.id
+		s.reservationStage.RUnlock()
+
+		for _, charID := range charIDs {
 			session := s.server.FindSessionByCharID(charID)
 			if session != nil {
 				session.QueueSendMHFNonBlocking(&mhfpacket.MsgSysStageDestruct{})
 			}
 		}
 
-		delete(s.server.stages, s.reservationStage.id)
+		// Delete from stages map under stagesLock (not nested inside stage RLock)
+		s.server.stagesLock.Lock()
+		delete(s.server.stages, stageID)
+		s.server.stagesLock.Unlock()
 	}
 
 	destructEmptyStages(s)
@@ -306,7 +328,10 @@ func handleMsgSysUnlockStage(s *Session, p mhfpacket.MHFPacket) {
 
 func handleMsgSysReserveStage(s *Session, p mhfpacket.MHFPacket) {
 	pkt := p.(*mhfpacket.MsgSysReserveStage)
-	if stage, exists := s.server.stages[pkt.StageID]; exists {
+	s.server.stagesLock.RLock()
+	stage, exists := s.server.stages[pkt.StageID]
+	s.server.stagesLock.RUnlock()
+	if exists {
 		stage.Lock()
 		defer stage.Unlock()
 		if _, exists := stage.reservedClientSlots[s.charID]; exists {
@@ -377,7 +402,10 @@ func handleMsgSysSetStagePass(s *Session, p mhfpacket.MHFPacket) {
 
 func handleMsgSysSetStageBinary(s *Session, p mhfpacket.MHFPacket) {
 	pkt := p.(*mhfpacket.MsgSysSetStageBinary)
-	if stage, exists := s.server.stages[pkt.StageID]; exists {
+	s.server.stagesLock.RLock()
+	stage, exists := s.server.stages[pkt.StageID]
+	s.server.stagesLock.RUnlock()
+	if exists {
 		stage.Lock()
 		stage.rawBinaryData[stageBinaryKey{pkt.BinaryType0, pkt.BinaryType1}] = pkt.RawDataPayload
 		stage.Unlock()
@@ -388,7 +416,10 @@ func handleMsgSysSetStageBinary(s *Session, p mhfpacket.MHFPacket) {
 
 func handleMsgSysGetStageBinary(s *Session, p mhfpacket.MHFPacket) {
 	pkt := p.(*mhfpacket.MsgSysGetStageBinary)
-	if stage, exists := s.server.stages[pkt.StageID]; exists {
+	s.server.stagesLock.RLock()
+	stage, exists := s.server.stages[pkt.StageID]
+	s.server.stagesLock.RUnlock()
+	if exists {
 		stage.Lock()
 		if binaryData, exists := stage.rawBinaryData[stageBinaryKey{pkt.BinaryType0, pkt.BinaryType1}]; exists {
 			doAckBufSucceed(s, pkt.AckHandle, binaryData)
@@ -412,7 +443,10 @@ func handleMsgSysGetStageBinary(s *Session, p mhfpacket.MHFPacket) {
 
 func handleMsgSysWaitStageBinary(s *Session, p mhfpacket.MHFPacket) {
 	pkt := p.(*mhfpacket.MsgSysWaitStageBinary)
-	if stage, exists := s.server.stages[pkt.StageID]; exists {
+	s.server.stagesLock.RLock()
+	stage, exists := s.server.stages[pkt.StageID]
+	s.server.stagesLock.RUnlock()
+	if exists {
 		if pkt.BinaryType0 == 1 && pkt.BinaryType1 == 12 {
 			// This might contain the hunter count, or max player count?
 			doAckBufSucceed(s, pkt.AckHandle, []byte{0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00})