Hello Jan
This is indeed a strange error. The first thing to check is if you have any port channel/etherchannel configurations on the device. I assume you don’t but check anyway. 
I would have to conclude that this is one of those strange behaviours of GNS3. Doing a search myself, I have found that one other person has encountered this very same issue, with private VLAN configurations on the NX-OSv on the Cisco Learning Network. Although no solution has been posted, the error is reproducible.
I suggest you take a look at some of the GNS3 posts that deal with PVLAN support and see what others have done to get it to work. Keep in mind that from what I gather, PVLAN is still not very stable in the GNS3 environment.
The only sure way at this point to get it to work is either to use real hardware, or to use VIRL which officially supports it.
I hope this has been helpful!
Laz