External storage module provides only Samba shares without authentification

I am trying to find a proper cloud storage for my Raspberry Pi 3. I tried several systems and nextcloud seems to be most reasonable for me. There are nice Android clients as well. I want to also share my Samba shares on the same server like the nextcloud server. However, something with the external storage app is broken. When i try to install the share as local file system, it denies to register, maybe because of the file permissions but maybe also because of some other reason. If i want to mount it as SAMBA share it only accepts the SAMBA shares with guest account allowed. And guest account is also configured to be the default fallback option for a failed authentification. My only SAMBA share that requires authentification is not mounted at all and the red light appears on the side always. As for now i feel little bit perplexed what happens here.

My SAMBA configuration is as follows:

usershare allow guests = Yes
map to guest = Bad User

comment = read access to Samsung harddrive
path = /mnt/samsunghd
guest ok = Yes

comment = public anonymous access
path = /mnt/samsunghd/public
create mask = 0660
directory mask = 0771
guest ok = Yes
read only = No

comment = SamsungHD for user pi rw
path = /mnt/samsunghd
read only = No
valid users = pi