Some examples:
You already fail to acknowledge the bug here on a smb connection: How to make Dolphin to access SMB share again?
KDE Bug, which they say was resolved in 2011 (!) with similar description: 209764 – dolphin can neither remember well nor forget the network places' passwords
Manjaro Forum without a clear solution: Dolphin: The file or folder smb://sharename does not exist - Network - Manjaro Linux Forum