Sometimes cannot move anything on timeline in some sessions

So I’ve been having this ‘bug’ on and off on this project and its infuriating. Basically I’ll load up a session sometimes and I cannot move anything - like drag audio or midi files around the timeline. I can otherwise do everything else and shortcuts and everything are fine. The tracks are not locked. There’s no hidden cubase dialogue open in the background that is taking over the focus. Nor is it anything to do with snap or having multiple files selected which cant move before the timeline. If I quit cubase and reopen the session things are absolutely fine. Then at some point when I reopen this session down the track it will just happen again. Again a quit and reload is fine.

Any ideas?