Yeah sorry, completely stock. I've done the factory data reset to no avail.
Which release? MI9, MJ7, MJE?
Does it crash randomly some time after you begin to use the phone or contacts app, or immediately upon entering one or both of those apps?
The logcat *might* contain some clues, dunno. It's a low-cost effort to capture it.
I suppose the next steps are to figure out whether it happens because of something peculiar about your data (contacts database / call & message logs/ etc), or if there is a problem with your hardware.
If you thought the trouble was a software bug that only showed up by getting triggered because of something unusual about your contact data, one way to see if that was the case would be to factory reset and bypass the google account setup** - and then use the phone or contacts app for a while without a connected Google account. (Set up a few phone-only contacts) and use the phone/contact apps that way.
If it still crashes, I would just go and get a warranty replacement on the phone - it's got to be under warranty still, yes? (Another option would be to use Kies or Odin to reflash all the stock phone software; but honestly, if you thought that the phone was acting strangely enough to do that it is probably a better bet to just get a warranty replacement).
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** maybe the effort of running a test like this could be simplified by just deleting the primary google account on the phone and clearing the data from the contacts/phone apps/services. But I've never tried that, and it's probably not quite equivalent to a factory reset trial.