If you haven’t already done so, go to File>Preferences>Audio Connections>Control Panel and see what the sample rate is on your soundcard device. I expect that it will be something other than 44.1kHz.The cause is that for some reason your soundcard is not resetting its sample rate.
Try opening a single 44.1 file in a tab. Play that. Then switch back to the montage. It will probably play.
I have had this happen once before (in a previous WL version different RME). Playing a file seemed to ‘reset’ the RME card.