This looks a bit like an issue I noticed recently where the display colour space wasn’t being applied correctly, and the view rendering would switch between two different colour spaces, seemingly at random. However, I only saw this in a Standalone app using the CoreGraphics renderer, and then only when there were two+ monitors attached, using different colour spaces. I thought this bug was fixed in the commit I linked above; however, I think incorrectly-applied colour-spaces are still the most likely cause of the behaviour in the video you linked.
I’ve tried running an AU in Logic 10.7.4 on M1 with multiple external displays, with and without OpenGL enabled, and then adjusting the display colour spaces. I can’t reproduce the flickering behaviour so far.
Unfortunately, I don’t think I’ll be able to make much progress on this without being able to reproduce the bug locally.
To track this down, it might be helpful to know whether the issue is present in the newest version of Logic (or, failing that, the exact version of Logic that the user has installed). It may also help to know whether the user has multiple displays attached, and if so, which colour spaces are active on each display (you could ask for screenshots of the Displays->Display Settings... pane from System Preferences). Finally, you could try building a copy of the AudioPluginDemo (or some other minimal plug-in) with OpenGL enabled, and sending that to the user to test. If the issue is also present in the AudioPluginDemo, then that would be an indicator that the problem is caused by something in JUCE (or the host) rather than Falcon specifically.