The plaster has detached while knocking the grooves...

The substrate must always be adapted accordingly. With Poroton or Ytong, less adhesion primer is needed, but deep primer is required to seal the strongly absorbent material. Here, the adhesion is ensured by the relatively rough surface.

Other substrates may not absorb as strongly; here, an adhesion primer is needed to facilitate adhesion. This is done when tiling over tiles. The adhesion primer is important here.

Or the top plaster on facades. It also needs adhesion primer. Usually, quartz sand and deep primer are combined to provide proper adhesion and sealing into the base plaster.

But I would definitely say that treating the Poroton substrate with deep primer is absolutely necessary for gypsum plaster.
Otherwise, just look at your bathroom; the plaster will come off again at some point.

Moreover, deep primer is not even expensive. You don't need a branded product. 10 liters costs maybe 12 euros.

Thank you for the info. Is the plaster base required by any standard?

It's not a drama, the plaster will hold as long as no one hammers around there.

Just test yourself whether a primer is on the Poroton. As I said, simply spray the stones with a spray bottle filled with water (glass cleaner bottle etc.). If the water soaks in immediately and sponge-like, there is nothing on it.
If it beads off after spraying several times, then a barrier is on it.