You have your GUI resolution set at 4K and this is disrupting the intended functioning of the whitelist. If you change your settings as prescribed below I think this will likely fix your issue. If there is still an issue then please post full logs uploaded from the My OSMC add-on as this will give us a more complete picture of exactly how you have your device configured.
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 or On start/stop
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.