Bind to external SMB not working

Hello,

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
nginx-1.12.2-1.el7_4.ngx.x86_64
libsmbclient-4.6.2-11.el7_4.x86_64
php-smbclient-0.9.0-1.el7.remi.7.1.x86_64
samba-client-4.6.2-11.el7_4.x86_64

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.