Zirconia crown moved after flossing

Roughly 3h after Zirconia crown installation I flossed which probalbly is a mistake(?)

Its 3 molars next to each other on lower right jaw, immediately after putting pressure with floss between teeth I can feel pressure like something is between the teeth, after a minute of panick I press with my fingers down towards the gum / jaw (this is how the dentist did at office), and after a while the tension went away.

These 3 teeth need to be shaven anyway as they are still too high.

Is it normal that the dentist spent 90 minutes grinding the zirconia crowns, he even had to grind my healthy teeth aswell.

He kept putting "dentist paper" for me to bite down on, but seemed clueless as on how good my bite is, kept asking "if now is good".

Is this normal?

I still need to go back to have more shaven off the 3 zirconia crowns next to each other, as they stop other teeth from connecting when biting with light force.

These are zirconia crowns from lab, it took 3 days to arrive at dentist office.