Just updated to the latest OSMC release - and at the same time updated from alpha5 to alpha10 using @hissingshark’s script (install from binary).
I imported my config and had to re-enable the capture the screen - and all works. Even the YouTube issue some people were having (4k doesn't work in the Youtube Addon) has gone away it seems.
Thank you @hissingshark for making this so easy 