[Brand new P2S] 50% OK / 50% FAIL

Hello everyone,
I've had a P2S for a few days now. It was easy to set up on a custom-built, stabilized stand.

I've done about ten successful prints, and just as many failures. Each time, it starts off well, then... a support detaches, the whole part shifts, and it's spaghetti.

I clean the build plate before each print with isopropyl alcohol, but it didn't help.

I tried hairspray (super glue, a little bit, and a good amount), but it didn't help.

I tried lower layer heights, but it didn't help, and a reduced speed (90mm/s), but it didn't help either...

So, at best, I'm getting about 50% success, and until I get to at least 90%, I refuse to do projects longer than 4 hours.

I only use PLA/PETG filaments from Bambu, and there's really only one that has never given me trouble: PLA MATE BLACK.

Where am I going wrong?

Thanks in advance!