Menu>Studio>Audio-Mixer pops up the mixer panel but all the channel numbers are invisible making it completely unusable. I marked the subject Tumbleweed but it’s more a rosegarden version problem (I think). On 13.2 I use version 16.06, the last one without this issue.
Try it with different user and check if the issue continues. This is a good way to start.
As another user I didn’t have the problem, so I looked at the problematic Rosegarden directory for clues. It was empty. I deleted it and let Rosegarden create a new one on takeoff, which it did and the numbers were there again. Interestingly the directory is still empty and while the menu fonts in the main window for example are consistent with desktop setting those in the mixer window are about 2mm in size and practically unreadable. Anyway, problem partly solved, thanks.
Check ~/.cache maybe
I presume that’s for the residual problem of small fonts in the Mixer window, clearing cache didn’t have any effect on that 