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I just tried my first 4K rip, using Lord of the Rings, and everything went well until I tried to play it on my TV off a USB drive. It plays for about 33 seconds, then goes back to the screen asking if I want to resume or start over. The files play fine on my PC. I reformatted the USB drive, ensured it was NTFS so file size wasn't an issue, and I tried 3 different parts of the movie.

I searched but haven't heard of this happening to anyone else like this. Is it more likely a problem with the speed of USB? My stick is USB 3, but the TV USB input speed is unknown, so might be 2.0. I suspect that's the issue, but wanted to ask if there are any other settings that I should look at?

I speculate that USB speed could be an issue. 4K movies are pretty big.

Can your PC play the file from the USB stick?

likely just the dumb tv "smart tvs" are junk use an nvidia shield or a computer hooked up to it.
usb2 is fine for 4K its 480mbps most movies just barely peak above 100mbps

you also could have a fake usb drive seen that quite a few times

I tested playing the movie from the same USB drive that was in my TV in a USB 2 port on my PC and it plays fine.

However, here is where it gets more interesting / crazy... I setup Windows 10 to be a DLNA server and shared the videos. I played a different video file and it worked fine. But with the LOTR 4K files, it does the same thing -- it plays around 33 seconds and quits. I tried it with both part 1 and 2 of Fellowship. Again, they play fine on my PC using VLC or Media Player.

I checked the specs on my TV again, which is 4K and HDR (a TCL with Roku OS), and in one place it says it supports MKV (H.264), although in another location it says it also supports MKV (H.265/HEVC). I figure LOTR in 4K is H.265, but if my TV doesn't support H.265, why would it play 33 seconds of the movie at all?

Any ideas what's going on here?

Pretty much all 4K UHDs are h.265 encoded video. MediaInfo can show you a lot details about files, including what kind of video encoding they have.

Does your TV play any other 4K UHD rips?

Decoding h.265 video is more computationally expensive than h.264 video.

In any case, before you spend a lot of time on this, think about if sneaker-netting movies to your TV via a USB stick is really the path you want to take. The convenience of running Plex, or Kodi, or whatever on a computer somewhere with the associated playback app running on your TV or on some kind of streaming box is very high.