Visited on May 29 and did a short charge with M-CHARGE RFID. No issue.
The M-CHARGE app indicated 3 available connectors, and the parking sign indicated "free" when I went down the ramp, but I found myself stuck behind another car that was waiting at the ticket gate. The machine indicated the parking was full and we had to wait for someone to come out. There is a little space next to the gate that allows turning around and leaving, which some people behind me did.
After waiting for a while, 2 cars finally exited and I was able to enter. I assume the charging spots don't count, because I found at least one available regular spot on that level. The charging station had 2 cars connected. One had finished charging and was no longer counted in the app, which is not good.
I charged for a short while, and we indeed got 25+25kW with the other car that was still charging.
To re-enter the parking on foot when the shopping center is closed there's a numpad outside the lift and door. I didn't get to try it, because other people were already re-entering and the door was open. I believe the code is on the ticket itself, but I didn't inspect very closely.
M-CHARGE app indicates always open but it doesn't seem to be strictly true, because you cannot enter between 22h and 06h. You can exit anytime.
Access to the building goes through a series of one-way street. Google shows Henric Petri-Strasse is also a one-way, but it doesn't seem to be true. You can turn left when leaving the parking to re-join Sternengasse.
I was not able to test the free parking logic as the store was closed. According to the signs, you get 30min free parking if you shop for at least 30CHF.