Sorry for the delay. I have not found the cause yet. I do not think we have tested it on 4.19 yet, so this might be a reason.
I thought the volumes will mount themselves without the
Lock->Unlock actions run in the Nitrokey App. Is that not the case?
@nitroalex Could you check that on the latest kernel - 4.19 - please? Just tested on Fedora with 4.18.16-200.fc28.x86_64, and it has not reproduced.