Rack instruments all red after audio interface was switched off and on

Your best bet is to reopen the last used rack or arrangement. Sometimes the Rebuild Rack command from the options menu also works.

I wonder thought, why this happens at all. This is the first time we see this outside our development environment. Any steps to reproduce? If so, this is a candidate for a fix and update.

That also happened yesterday in my computer. In Synfire standalone after audio reset because of a note sustained. I had to setup the default rack and recover from a previous backup.

If you have a procedure that reliably reproduces this, I'm confident we can fix it quickly.