Experiences with "shower tray elements with acrylic surface"

Our acrylic shower tray always moved a lot when standing on it. Then the joints came loose (see picture), water got under the tray, ...

that smells like a "design flaw":

The tray shell must, of course, rest flush all around everywhere without any significant play.
I had built this installation substructure (which remains invisible) from Ytong blocks and tiled it.
In the middle, I also installed a support against sagging (diagonal corner tray).

Our sink is acrylic. Since scrubbing with Vis or ata doesn't work, I clean it with Persil. Put in Persil, add some water, let the lye sit for 15 minutes, drain, wipe, clean.

that smells like a "design flaw":

Actually, the plumber who came and repaired it said that the tub was simply propped up with some stones. And they shifted or gave way. So indeed shoddy workmanship. Meaning: because acrylic gives more, the substructure must be done especially carefully or the builder must supervise this as far as possible. Small anecdote on the side: The same problem occurred earlier in another apartment here in the multi-family house. There, the general contractor brazenly accused the couple of having fun together in the shower too often and causing the whole thing :)