invisible obstacle

since a few weeks I have an obstacle on my land. I can't see it and I can't remove it. But when I walk over my land I can't pass through it. At least I have removed all from my land, but when I check the objects in about land, I see there are still 5 prims on it. But when I do "show" nothing is indicated. When I do "return" I receive the message that it is returned to my inventory. but no ... it is still there.
Who can explain it to me, or better, who can help me to remove it?

This is a farely common problem, The object in question is referred to as a ghost. The solution is to have the sim restarted. If you can't do this, or don't know someone who can you just have to wait till it is restarted.

(or you know... you "accidently" crash the sim and it restarts )

I have been at fireworks competitions that almost always incur accidental SIM restarts

So, if I understand well, the problem will disappear automatically
thanks, I'll remember your name for the next problem

Not quite. If you're on mainland, put in a support ticket to have the sim restarted. If on a private sim, contact an estate manager or the sim owner to have them restart it.

All sims are restarted EVENTUALLY for various reasons, but it could be weeks or even months until yours is.