Same issue here on macOS Ventura 13.5.2 (Mac mini M2 Pro), using JUCE 7.0.4 or 7.0.5.
I tried to update to 7.0.6, 7.0.7 or the latest develop (5e52056b9), but I have a different crash (assertion fail) happening right away when loading the MultithreadingDemo:
I use similar code in my plugin, which obviously reproduces the same behavior.
Is there an alternative to the MessageManagerLock that would work properly until this is fixed ?
Sorry this took so long, we found another relatively serious issue with the MessageManagerLock unfortunately that fix isn’t merged yet but I’ve merged something that should at least prevent the jassert you were seeing.
I’ll try to keep you posted regarding the other issue we found.