I have same problem, but TV is Philips UHD android 65".
For me directly from NAS is not an option, because TV manufacturers vere so cheap, they used 100M ethernet adapter (although gigabyte adapters were invented more than 20 years ago) and wifi also is slow, AC do not work at all. That means maximum quality UHD movie will not stream through that bottleneck without buffering from time to time. My USB3 is fast enough.
Some high bitrate UHD movies will work fine and some freese video app at about 40 minutes (not enough experience on low bitrate). Depends on a movie, if some movie stops at 43min and 22sec, then if after a reboot I fast forward (on Philips it is slow forward only) to the point where movie stopped, then hit "play" and after another 43:22 time has passed same thing happens. That means I can watch specific movies with 40 minute parts.
There are some opinions (not confirmed) that it is some kind of anti piracy thing, but it has no logic in it, but it cannot be overheating of some controllers, because stop times are too similar. If it is anti piracy, it should be confirmed officially, so that people will not waste time on working these problems.
Now I use timer to watch UHD movies. Set it to ~40min, if it rings, I just exit from player and quickly hit "continue" again and another ~40 min can go without any problems. Better than rebooting TV and slow-forwarding to the stop point.
I hope there will be a solution, it is annoying, but it is not only Sony thing.
