4K Video stopped playing on RPi 4 b OSMC

Try setting your GUI resolution to 1080p 60hz and see if that fixes it. If not try commenting out allowing 4k60 in your config-user file and see if that makes a difference.

More Info

We recommend people with 4K TVs set their user interface (UI) to 1080p. Kodi’s UI is not optimized for 4K yet and this can put unnecessary demands on your device and can lead to a suboptimal picture quality, as well as potentially cause other issues.

The settings we recommend are as follows…

Settings>System>Display>Resolution> 1920x1080p
Settings>System>Display>Whitelist> (empty) *
Settings>Player>Videos>Adjust display refresh rate>Always

Some televisions may also need, or benefit from, the following being set…

System>Display>Force 4:2:2 colour subsampling> (enable)

With the above settings your UI will be output in Full HD and your 4K content will be output in 4K.

*Information regarding the whitelist can be found here. If you have any doubt, feel free to upload some logs so we can verify that your settings are indeed correct.