Bind to external SMB not working


I am not able to connect Nextcloud to external SMB running on Windows Server 2016.
Unfortunately I do not get any error meassage that gives me any hint where to search.

nextcloud 12.0.3
CentOS 7.4

When I connect from CLI by smbclient it is possible by using parameter -m to connect using SMB2 as well SMB3. But somehow in Nextcloud I only get a red square as error and no error message.

Any idea where to search?

Suddenly it is working.
I have not changed annything and I do not know what was wrong. But suddenly connection to SMB is working.