I've searched to no avail.  Fresh reinstall, and when I take off all seems well then all of a sudden I'm hitting the ground in spots despite climbing, and ATC will tell me to climb to 14000 feet, used B key to set baro, then ATC is telling me I'm 800' above altitude and to increase my decent to 14000 feet when I'm at 14000 feet!  Any ideas?

I noticed that too after the update. I just finished the flight where I was at FL280 but ATC was like no, bro, you're 400ft below your assigned altitude, climb to FL280. I never had this issue before.

Noticed it too yesterday after SU5. I think it’s addressed today in the hotfix. Testing right now and will report back I here if I still see the anomaly. 
-Braun

Yep it's a bug that should be discovered and fixed quickly, maybe in the hotfix.

Seems fixed now, at least for me. Been spending the last 90 minutes flying and reflying a short hop I did yesterday to test FBW a320 with SU5. After downloading the latest DEV version per FBW and applying the hotfix, I no longer am getting altitude anomaly’s, at least so far, and I can confirm because each time it happened at cruising altitude (alt shift), the FBW autopilot would alarm and squawk continuously until it refound it’s programmed altitude. 

As I said, yesterday about every 10 min or so at cruise. Today, none so far!
-Braun

Great!  I had a little trouble getting the hotfix to appear in the Store but alas it just did so I just installed and didn't have a chance to fly yet.  I'm pretty stoked there are a lot of nice improvements in SU5.  To be frank it's been this way largely since day 1, w/ all updates solving more problems than they create.  I think the socalled performance update is quite remarkable all in all.  I mean the visual penalties for the performance increases seems like overall a big improvement, while there will be some robbing peter to pay paul in it, the net change is positive for me thus far.  I might not even install a brand new 3080Ti depending on how things look in the big dense areas and airports.