GET requests sometimes result in 500 Internal error responses

I use an Ambry instance for saving and serving media files (images and videos), and start having problem with some requests failing with status: 500 Internal Server Error and following exception trace in the log:

    [2017-10-10 16:02:52,366] ERROR Internal error handling request /AAEAAQAAAAAAAAAAAAAAJGExMDlhYWFjLWNjNGYtNDVjOS04ZjliLTUxMDY0MTdhZWY5OQ with method GET (com.github.ambry.rest.NettyResponseChannel)
    com.github.ambry.rest.RestServiceException: com.github.ambry.router.RouterException: Timed out waiting for a response Error: OperationTimedOut
            at com.github.ambry.frontend.AmbryBlobStorageService.submitResponse(AmbryBlobStorageService.java:322)
            at com.github.ambry.frontend.AmbryBlobStorageService$GetCallback.onCompletion(AmbryBlobStorageService.java:786)
            at com.github.ambry.frontend.AmbryBlobStorageService$GetCallback.onCompletion(AmbryBlobStorageService.java:698)
            at com.github.ambry.router.NonBlockingRouter$1.onCompletion(NonBlockingRouter.java:155)
            at com.github.ambry.router.NonBlockingRouter$1.onCompletion(NonBlockingRouter.java:149)
            at com.github.ambry.router.NonBlockingRouter.completeOperation(NonBlockingRouter.java:392)
            at com.github.ambry.router.GetBlobOperation.abort(GetBlobOperation.java:146)
            at com.github.ambry.router.GetBlobOperation.poll(GetBlobOperation.java:263)
            at com.github.ambry.router.GetManager.poll(GetManager.java:155)
            at com.github.ambry.router.NonBlockingRouter$OperationController.pollForRequests(NonBlockingRouter.java:522)
            at com.github.ambry.router.NonBlockingRouter$OperationController.run(NonBlockingRouter.java:575)
            at java.lang.Thread.run(Thread.java:748)
    Caused by: com.github.ambry.router.RouterException: Timed out waiting for a response Error: OperationTimedOut
            at com.github.ambry.router.GetBlobOperation$GetChunk.cleanupExpiredInFlightRequests(GetBlobOperation.java:553)
            at com.github.ambry.router.GetBlobOperation$GetChunk.poll(GetBlobOperation.java:530)
            at com.github.ambry.router.GetBlobOperation.poll(GetBlobOperation.java:232)
            ... 4 more

• Ambry version: recent built from commit e1a688eccb040934c3e6e94281da6c2b9826522d
• JVM version: 1.8.0_131

Start with the stack-trace entry points in AmbryBlobStorageService.java, NonBlockingRouter.java, and GetBlobOperation.java, focusing on GetChunk cleanupExpiredInFlightRequests and the OperationTimedOut path. Reproduce or trace the failing GET and determine the cause of the timeout and the expected handling of the response; done should include a verified resolution for the reported 500 errors.