Is UndoManager thread safe?

A tester reported a crash. From the OSX crash log I can see, that two threads are trying to call UndoManager::perform at the same time. Thats when it crashes.

Therefore I am wondering: Is the JUCE UndoManager class thread safe?

The AU was built with JUCE 6.0.1 in OSX Catalina.
The plugin was run under OSX Catalina & Logic 10.2.4.