Or are you moving the file, or recording directly to a network drive. That might be the problem, in which case using the above is suggested practice, i.e. record to local content folder, then with the above Module configured Wowza will move the file when recording is finished.
If you are already moving after record, might be related to the move, in which case it would be a network problem during that move, but it is more likely just a bad recording, which does happen occasionally, also probably due to network problems. If you were recording to an .mp4 container you would see a .tmp folder with the same name in the content folder where the stream was recorded to file. The .mp4 file in that case is not recoverable.
Otherwise, can you replicate this, does it happen consistently?
I'll do some more tests to check and see if the .tmp files are existing. However, the question would still remain that I have three different servers:
Server A running version 3.5
Server B & Server C running version 3.6.2
All 3 are writing to a fourth server (server D) and are all on the same network.
Server A works perfectly, servers B & C don't. A network issue seems highly unlikely. Was anything changed between those versions in regards to how you write the files or process the header when the file write is completed?