Can't click hotbars

Hi there! My partner and I play the game together, and lately she's been having a problem for a short period after she logs in where she can't click her hotbars. The numbered ones work, but hotbars without associated hotkeys are completely unresponsive.

It's not a character issue, because I logged in on my account on her machine and the problem remained.

Furthermore, it 'fixes' itself if you call a mount from the mount guide. The hotbar(s) is/are locked, so it's not a case of them accidentally being dragged. Other things can be clicked just fine.

Any idea what this is? Is there a fix?