Quick update.
Sent logs etc to support. I did find when/where this exactly happens, as it seemed random at first. It is as soon as you press play (spacebar) when the main MIR window is in focus. I even loaded an empty software track - loaded MIR plugin - raised the window - press play = crash.
So, as long as you don't press play with that main window is open it's fine. I could add tracks etc. Even open the main GUI and move instruments, settings etc. Close the window. Press play and all fine. It's something when the GUI is open and you hit spacebar.
See what they come back with. 👍
edit: couldn't get this to crash on 10.4 using the above method. Every time under 10.5