Hi Benjamin,
I have no Mac, but indeed it sounds like it is a computational problem. Possible culprits are other plugins (XSquawkbox is also a plugin!), anti-virus programs (on Windows the Windows Defender is definitely causing problems in a MOD state), an outdated operating system, background programs running or heat issues (cores throttling down).
Since it seems to happen on every route for you and other people on Mac are flying just fine, I don´t think it is a problem with the code per se. Yes, we will look into optimizing the MOD state calculation process in the future, but for most people this seems to be no problem, so I think we have to look at your specific setup for the solution to your problems.
Hang in there and let me know if you make any discovery per the above points, Jan