Periodic interface slowdown – playback fine

I am experiencing periodic slowdowns in the GUI when browsing media. It is like the refresh rate is dropping to 10fps or something (I have the GUI set to 60fps). Initially it is fine, it appears to happen after stopping playback of a video and going back to browse the library. Playing a new video, refresh rate is fine and unaffected. Reboot, and is also fine and back to normal. This is on a recent libreelec nightly build, on a i5 NUC. It’s only started doing it in the last couple of weeks. It is the same whether the media initially played is local from NAS, or YouTube plug-in.

Any ideas? I will try and recreate and post a debug log later (although the first time I enabled debug logging, it didn’t seem to do it anymore…)

Thanks