I’ve got the same problem, with a MOTU Ultralite mk3 Hybrid audio interface connected over FireWire. Like OP, the Mac’s internal audio output works fine, but when switching back to the external interface there’s no more sound. Renoise also beachballs for maybe half a minute when switching to the external interface. I haven’t experienced audio issues in other applications.
Another annoyance that’s new with Mojave is that the first time you start it, you get a system popup telling you that Renoise wants to access your contacts. I’m guessing it’s because the application is blindly iterating through ~/Library/Application Support, since in the system log there’s some access control error messages about Renoise also being denied access to locations like ~/Library/Application Support/CallHistoryDB. There doesn’t seem to be any harm in denying access, but it’s a bit surprising and scary to see a popup like that, since there’s so many applications that try to steal your private data.
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