Dolphin suggests you are using KDE.
Try installing the packages gvfs and gvfs-smb
You could try to use
gio mount smb://server/share
I know you say is has worked - so check the file - you should have something specifying the dialect (NT1 being the deprecated SMB1) - the file is a requirement - albeit content is not ![]()
/etc/samba/smb.conf
[global]
min version = NT1
workgroup = WORKGROUP