The vapor barrier has a brownish position, insulation is wet

Classic case.

Climate membrane with variable SD value sealed from below and above with OSB.

The house has probably already been plastered inside?

The moisture from plastering and laying the screed (which has not yet been done in your case) rises through the climate membrane into the insulation. However, this is such a large amount and the room below is still damp that the room air cannot release moisture. Then the insulation wool keeps absorbing more and more moisture. Probably especially a lot in one spot because it was likely executed incorrectly there.

According to the manufacturer’s specifications, for example from the Ursa climate membrane including insulation, this may only be installed after plastering and screed have been applied. The residual moisture in the rooms should also be low. So first let the building dry, then install the insulation with membrane.

I would only make the holes after consulting with the construction supervisor. Not that the whole thing backfires. It is quite possible that the problem only exists during the construction phase; as saar2and described it, it sounds plausible.

We had the problem that a conduit was lying on the insulation and the moisture rose and spread wonderfully.

I also see that as a logical response from saar2and.

Yes, the plaster is already applied inside, the screed will follow next week.

If that is the case, then the whole thing should work again as soon as the moisture in the rooms has decreased, so that the moisture is released back into the room or the gypsum board of the suspended ceiling?

Do you possibly have a value that should prevail in the insulation layer? I am considering installing something like a permanent meter there, also to be able to act later, even when the ceiling is then suspended.

Theoretically, it should work with a probe of temperature and humidity sensors for household use. You just place the probe between the insulation and observe the whole thing. The only problem is that eventually the battery will be dead. Supplying the transmitter with power continuously could be difficult due to fire protection. Maybe also because of the costs. The question is how meaningful point measurements are at all; an expert could know that. One value is likely to be individual here. It is said that below 70% indoor humidity there is normally no mold, but it might be different in the insulation. I once read something about 60% (but I am an amateur!!). But it could be that potential condensation occurs then and that is not interpreted correctly?

As soon as insulation gets wet, it is ruined. NO MATTER WHETHER glass wool or rock wool. The spot that was once damp (wet) should allow the vapor barrier to dissipate as much moisture as possible but will always have worse insulation than the rest and could therefore be a thermal bridge. And if the wood above it is already wet/was wet, then that is not a small amount of water. And screed is even worse than plastering. My tip: remove everything and after the screed put back in whatever is still usable.