Camera tracker stuck at initializing.

It sounds like you're running into a bug with the Camera Tracker on ultra-wide comps. This issue can happen due to memory or GPU load with large comps like 6400x1800. One possible fix is to precompose your shot into a smaller resolution or proxy version for tracking, then apply the solved camera to the full-res comp GPS.

I struggled with this issue for about a day.  Finally purged my Image cache (along with Memory & Disc cache) and the 3D camera tracker went back to working as normal.

Hope this helps some of y'all - shame that Adobe leaves it up to us paid users to sort out their issues, especially after years of complaints!

Same issues but on a M2 Pro Mac mini. 4K footage. I've tried clearing the cache, resetting preferences, shortening clip, using Pro Res version etc.. still does the same thing. Stuck at initializing 24hr +. 
Any ideas, ..anyone?

Have you considered generating a smaller version and track that? 3D tracking isn't really dependent on absolute coordinates and you could scale the scene. It might also be worth trying to pre-compose to a more conventional aspect ratio. Perhaps it's just the extreme field of view in a towel strip that wacks things out...

Mylenium 

Hard to say, but of course the usual culprits should be checked first: graphics driver, hardware acceleration settings, cache settings, temp folders. In your case you may also want to turn off multiframe rendering. At such large resolutions you easily run out of memory and somehow I have the gut feeling that this is a problem of the additional AE render processes lingering around and clogging up the system rather than the tracker itself.

Mylenium