KDE does not save screen resolution on linux mint 18, save the resolution and restart the resolution back to the unwanted ...
Which Plasma version? Could you please also show the kscreen log and configuration files after changing them, and if they get modified after a restart? See ~/.local/share/kscreen/
If you can provide the information requested in comment #1, please add it.
To further investigate this issue, KDE developers need the information requested in comment #1. If you can provide it, or need help with finding that information, please add a comment.
No response, changing status. If you have new information, please add a comment.