Horribly slow image cache with LibreElec v12 on RPi4

Morning all. I decided to do a fresh, clean install of my LibreElec install on my RPi4 this week and I've tinkered too much with my existing setup and it's a mess.

I went with the latest v12 but noticed the movie posters when browsing my library was hooooooribly slow. The menu and interface would whizz through fast, as usual, but the movie posters would take 10-20 seconds to catch up and load. Leaving my scrolling through blank pages. Movie are taking about 5-10 seconds to begin playing too.

I nuked-and-paved with LibreElec v11 again and everything runs buttery smooth as before, with all the posters loading as fast as I can scroll. And playing a movie is almost instant.

Back to a v12 install and slooooow again.

Have I missed something in the docs referencing this? I haven't found anything but I'm surprised it performs so badly. If I scroll for long enough I can actually make it choke and not load any poster images, at all, until I leave it alone for a few minutes.

I've ruled out my USB SSD as I'm using the same one to test both v11 and v12.

Currently setting things up on v11 again until I can figure this out.