Re: "US, Canada finally ground 737 Max jets..."
From what I've been reading over the last few days, there has been evidence aplenty, particularly for South West Airlines pilots that MCAS is a pig and Boeing have been working on a patch for some while because they already know there are issue with MCAS.
Yes, apparently pilots have reported quite a few issues with MCAS.
You would think, that in light of that, perhaps better documentation/warnings should have been distributed by Boeing/FAA to be absolutely crystal clear to any operators of the aircraft what those issues are and how to address them. Especially since failure to do so is likely to result in rapid disassembly of the aircraft.