Collabora on mobile can't save edited documents in shared folders

Hi, I use collabora online and NC 17.
On a shared folders changes on office documents are only saved except for the folder owner.
User to whom the owner gets access can only create the file, but all the changes aren’t saved. Message: “The document could not be saved”
This only applies for mobile access, on the web it’s working.

Would be awesome if someone get me a hint