I think the fact that your Documents folder is being backed up by OneDrive is most likely the cause f your problem.
It's a personal preference but one of first things I do when I install/reinstall Windows on a system is uninstall OneDrive.
The ultimate solution would be for JuiceboxBuilder to pick a different location for the .tempGallery folder but, unfortunately, this is hardcoded into JuiceboxBuilder and not user-changeable.
All you can do is persevere to try to exclude your Documents folder from OneDrive (or disable/uninstall OneDrive completely).
There seems to be a lot of people online wanting to exclude Documents from OneDrive. Maybe these links will help:
https://www.tenforums.com/general-suppo … drive.html
https://www.tenforums.com/tutorials/290 … -10-a.html
Even if you cannot exclude the entire Documents folder from OneDrive, maybe you could exclude the JuiceboxBuilder-Pro folder inside Documents.