diff --git a/app/controllers/cwmp_controller.ts b/app/controllers/cwmp_controller.ts
index 1926c69..dbecf0c 100644
--- a/app/controllers/cwmp_controller.ts
+++ b/app/controllers/cwmp_controller.ts
@@ -81,6 +81,7 @@ export default class CwmpController {
 
       if (message?.type === 'TransferComplete') {
         const hashId = manager.getHashIdForRemote(remoteKey)
+          ?? manager.getHashIdForRemoteIp(request.ip())
         if (hashId) ctx.cwmpDeviceId = hashId
         logger.debug({ sessionId, hashId }, 'CWMP sending TransferCompleteResponse')
         const resp = buildSoapEnvelope(
@@ -92,6 +93,7 @@ export default class CwmpController {
 
       manager.ensureSessionForRemote(remoteKey, sessionId)
       const hashId = manager.getHashIdForRemote(remoteKey)
+        ?? manager.getHashIdForRemoteIp(request.ip())
       if (hashId) ctx.cwmpDeviceId = hashId
 
       if (message && manager.hasSession(sessionId)) {
diff --git a/app/middleware/cwmp_logger_middleware.ts b/app/middleware/cwmp_logger_middleware.ts
index f903ff3..4395fdb 100644
--- a/app/middleware/cwmp_logger_middleware.ts
+++ b/app/middleware/cwmp_logger_middleware.ts
@@ -34,12 +34,15 @@ export default class CwmpLoggerMiddleware {
     const { request, response } = ctx
     const rawBody = request.raw() || ''
 
-    const socket = request.request?.socket
-    const remoteIp = request.ip()
-    const remotePort = socket?.remotePort || 0
-    const localAddress = socket?.localAddress || 'unknown'
-    const localPort = socket?.localPort || 0
-    const sessionId = `${remoteIp}:${remotePort}->${localAddress}:${localPort}`
+    // Reuse sessionId already computed by CwmpMiddleware to avoid drift
+    const sessionId = request.cwmp?.sessionId ?? (() => {
+      const socket = request.request?.socket
+      const remoteIp = request.ip()
+      const remotePort = socket?.remotePort || 0
+      const localAddress = socket?.localAddress || 'unknown'
+      const localPort = socket?.localPort || 0
+      return `${remoteIp}:${remotePort}->${localAddress}:${localPort}`
+    })()
 
     let capturedResponseXml: string | null = null
     let isEmptyResponse = false
diff --git a/app/services/cwmp/state_machine_manager.ts b/app/services/cwmp/state_machine_manager.ts
index d1650c7..6976622 100644
--- a/app/services/cwmp/state_machine_manager.ts
+++ b/app/services/cwmp/state_machine_manager.ts
@@ -40,7 +40,8 @@ export class StateMachineManager extends EventEmitter {
   private machines: Map<string, StateMachineInstance> = new Map()
   private deviceSessions: Map<string, string> = new Map() // deviceKey -> sessionId
   private sessionMachines: Map<string, string> = new Map() // sessionId -> machineId
-  private remoteToDevice: Map<string, string> = new Map() // remoteKey -> deviceKey
+  private remoteToDevice: Map<string, string> = new Map() // remoteKey -> deviceKeyJson
+  private deviceToRemotes: Map<string, Set<string>> = new Map() // deviceKeyJson -> Set<remoteKey>
   private cleanupInterval: ReturnType<typeof setInterval> | null = null
 
   private static instance: StateMachineManager | null = null
@@ -221,10 +222,31 @@ export class StateMachineManager extends EventEmitter {
   }
 
   /**
-   * Bind a remote endpoint to a device for session rebinding
+   * Bind a remote endpoint to a device for session rebinding.
+   * Maintains the reverse index deviceToRemotes for O(1) cleanup.
    */
   bindRemoteToDevice(remoteKey: string, deviceId: DeviceId): void {
-    this.remoteToDevice.set(remoteKey, JSON.stringify(deviceId))
+    const deviceKeyJson = JSON.stringify(deviceId)
+    this.remoteToDevice.set(remoteKey, deviceKeyJson)
+    let remotes = this.deviceToRemotes.get(deviceKeyJson)
+    if (!remotes) {
+      remotes = new Set()
+      this.deviceToRemotes.set(deviceKeyJson, remotes)
+    }
+    remotes.add(remoteKey)
+  }
+
+  /**
+   * Remove all remoteToDevice entries for a device. Called on session completion/failure.
+   */
+  private unbindRemotesForDevice(deviceKeyJson: string): void {
+    const remotes = this.deviceToRemotes.get(deviceKeyJson)
+    if (remotes) {
+      for (const rk of remotes) {
+        this.remoteToDevice.delete(rk)
+      }
+      this.deviceToRemotes.delete(deviceKeyJson)
+    }
   }
 
   /**
@@ -249,28 +271,54 @@ export class StateMachineManager extends EventEmitter {
   }
 
   /**
-   * Fallback lookup: returns the hash identifier for any active device whose
+   * Fallback lookup: returns the hash identifier for a RUNNING device whose
    * last known remote IP matches the given IP (ignoring port).
    * Used when a CPE opens a new TCP connection for an empty POST and the
    * exact remoteKey (IP:port) is not in the map.
+   *
+   * Only considers devices with an active (RUNNING) state machine to avoid
+   * returning a stale or wrong device under NAT/CGNAT scenarios.
+   * Returns undefined if zero or multiple RUNNING devices match the IP.
    */
   getHashIdForRemoteIp(remoteIp: string): string | undefined {
+    const candidates: string[] = []
+
     for (const [key, deviceKeyJson] of this.remoteToDevice.entries()) {
-      const keyIp = key.split(':').slice(0, -1).join(':') // strip port (handles IPv6 too)
-      if (keyIp !== remoteIp) continue
-      try {
-        const deviceId = JSON.parse(deviceKeyJson)
-        return getDeviceHashIdentifier({
-          manufacturer: deviceId.manufacturer ?? '',
-          oui: deviceId.oui,
-          productClass: deviceId.productClass,
-          serialNumber: deviceId.serialNumber,
-        })
-      } catch {
-        return undefined
+      // Strip port: for IPv4 "1.2.3.4:port" → "1.2.3.4"
+      //             for IPv6 "[::1]:port" → "[::1]" (request.ip() returns without brackets)
+      const lastColon = key.lastIndexOf(':')
+      const keyIp = lastColon > 0 ? key.slice(0, lastColon) : key
+      // Normalize: strip brackets if present so "[::1]" matches "::1"
+      const normalizedKeyIp = keyIp.replace(/^\[|\]$/g, '')
+      if (normalizedKeyIp !== remoteIp) continue
+
+      // Only consider devices with a currently RUNNING session
+      const existingSession = this.deviceSessions.get(deviceKeyJson)
+      if (!existingSession) continue
+      const machineId = this.sessionMachines.get(existingSession)
+      if (!machineId) continue
+      const machine = this.machines.get(machineId)
+      if (!machine || machine.status !== MachineStatus.RUNNING) continue
+
+      if (!candidates.includes(deviceKeyJson)) {
+        candidates.push(deviceKeyJson)
       }
     }
-    return undefined
+
+    // Ambiguous under NAT/CGNAT: refuse to guess
+    if (candidates.length !== 1) return undefined
+
+    try {
+      const deviceId = JSON.parse(candidates[0])
+      return getDeviceHashIdentifier({
+        manufacturer: deviceId.manufacturer ?? '',
+        oui: deviceId.oui,
+        productClass: deviceId.productClass,
+        serialNumber: deviceId.serialNumber,
+      })
+    } catch {
+      return undefined
+    }
   }
 
   /**
@@ -470,6 +518,7 @@ export class StateMachineManager extends EventEmitter {
     const deviceKey = JSON.stringify(machine.deviceId)
     this.deviceSessions.delete(deviceKey)
     this.sessionMachines.delete(machine.session)
+    this.unbindRemotesForDevice(deviceKey)
     // Drain any leftover tasks so they don't bleed into the next session
     this.taskQueue.clearPendingTasksForDevice(machine.deviceId)
   }
@@ -480,6 +529,7 @@ export class StateMachineManager extends EventEmitter {
     const deviceKey = JSON.stringify(machine.deviceId)
     this.deviceSessions.delete(deviceKey)
     this.sessionMachines.delete(machine.session)
+    this.unbindRemotesForDevice(deviceKey)
     logger.error(`State machine failed: ${error}`)
   }