Short story... trying to look for an IRP by following the steps listed here https://blogs.msdn.microsoft.com/ntdebugging/2011/11/23/where-did-my-disk-io-go/
without luck. The IRP is not in the outgoing packets and the original IRP is not completed.
Long: My driver makes a call to FltCreateFileEx (targetting a VHD volume) and stops in the call to NtfsAcquireExclusiveFcb owned by another thread which called NtFlushBuffersFileEx which ends in a call to DiskFlushDispatch/ClassSendSrbSynchronous that could track until VHDMP.SYS ... don't know what this driver internally do/did to the request. (checked all threads involving storport/vhdmp/disk/classpnp)
On the other hand I have several threads locked in NtfsCheckpointVolume and a worker thread that called NtfsCheckpointAllVolumes stopped in ClassShutdownFlush/DiskShutdownFlush.
No locks being held except the one for Fcb access.
Any hint on where I can continue my research will be appreciated.