I have a DS-2CD2132F-IWS (Original, no CN model) to, upgraded it to 5.4.5, and the network disconnects are back (tried 5.4 before with the same result)!
Just after a few hours, after an power cycle the errors start and the camera is not responding anymore.
The downgrade from 5.4.0 to 5.3.0 I did...