Unfortunately that sounds like it could be a hardware issue.
To rule out anything with firmware – store a show as a backup, carry out a firmware reinstallation and then a hard reset.
If this doesn’t help, then please contact your local distributor to arrange to have your SQ serviced/repaired.
You can find the full list of our distribution partners here – https://www.allen-heath.com/where-to-buy/
I had same issue a few years back and reseated the ribbon cables to the fader board and that solved the issue for me. You’ll need to remove the bottom cover to access them. Hope this helps.