MainStage stops responding to next patch and previous patch messages

Twice during dress rehearsal I had MainStage stop responding to "next patch" and "previous patch" controller moves. I have a foot-switch sending controller #16 triggering "next patch" and have the lowest key on my 88-key controller triggering "previous" patch. It works great, but at some random point MainStage stops responding to those messages.

I use the cursor to try selecting a patch in the list (I'm in Performance mode) and I cannot select a new patch there either. I have to force quit and restart MainStage to get functionality back. I'm running 3.4.2 on a MacBook Pro from 2010 that cannot install Mojave.

Anyone else experiencing something similar?

Thanks!

--Kurt Cowling