Track I/O Input Select Button Frozen / Locked?

[weirdfriend]

Hi, I'm new on the forum, posting for the first time because I haven't been able to find an answer after an hour of searching... so please go easy on me if I'm posting in the wrong place or this has already been answered :)

In both the mix and arrange windows, when I click the track input selector under I/O, the drop down menu isn't appearing. It works as normal for the track output selector.

The audio track inputs are auto assigned to Mic/Line 1, Mic/Line 2, etc and recording + input monitoring are working fine, so I don't think it's an I/O setup issue. I just can't reassign track inputs, or assign inputs to new Aux tracks.

When I create a new session it doesn't have this issue at first. However when I import all the tracks from the problem session into the new session, the new session starts having the same issue as well.

I think I probably just changed some setting or pressed a keyboard shortcut by accident, but I can't figure out what it was. Or maybe it's a corrupted session?

Any help would be much appreciated! Still learning PT, trying to switch from Logic but things like this keep tripping me up.

2018 Macbook Pro, OSX 10.14.6, PT 2021.3.1, RME Fireface UCX