Is this a similar situation?
https://forum.kicad.info/t/unexpected-char-error-in-gerberview/
As in this case, if you don’t write down the steps so that anyone can reproduce the issues, it will end up being like a quiz show question.
It would be best to “list in order the operations” you performed with the mouse.
Perhaps you launched Gover Viewer from the KiCad Project Manager, and then opened the zip file by selecting “File”->"Open Zip Archive FIle"from the Gover Viewer menu?
and … How did you create that zip file?
I assumed that the zip file contained files unrelated to the Gerber data. Is that actually the case?