versionText:SetPoint ("topright", PlaterOptionsPanelFrame, "topright", -25, -7)

This gives no errors for me

This will be fixed in an upcoming (alpha) version, but it appears that your UI-Addon is leaking a global frame variable.
Edit: you should run a /dump frame and check what is printed with your addon enabled/disabled.

@ViksUI This one most likely (or similar):
https://github.com/ViksUI/ViksUI/blob/70d0c40c06ae30b67f9d28a00c0acc06b25bbfeb/ViksUI/Modules/Chat/CopyChat.lua#L20 If you fix this, the error should be gone. Plater is causing no harm when this, or other frame variables are not global.
That one is actually defined in the file.

@ViksUI This function causes the issue:
https://github.com/ViksUI/ViksUI/blob/79889f64de6949db7c235d611d0c3812d6072ee6/ViksUI/Modules/UnitFrames/lib.lua#L117
All those functions should not be global, but local to your addon.
Edit: same goes for this one:
https://github.com/ViksUI/ViksUI/blob/79889f64de6949db7c235d611d0c3812d6072ee6/ViksUI/Main/Core.lua#L281

Thank you. Yes you are right about that. I made thos locals and all fixed. The last changes you made to Plater also worked fine.