I think I’ve actually found another solution. I was asking ChatGPT for help troubleshooting (why not … 
) and it suggested CoreELEC which I did recognise and am sure I used it before I went OpenELEC, LibreELEC and OSMC. There is a build for the S905D as well and it seems to be working other than a popup message that appears for ~30 seconds after a reboot and says:
CoreELEC DT-ID not found. Please update /flash/dtb.img
It doesn’t seem to affect anything though as far as I can see so far and the Blu-rays all play perfectly. I haven’t plugged in any speakers yet but I will try that later and if that works then I think I’m good.