Hi, as first, thanks for bug report and sorry for this complication. We will try to replicate it and fix it.
To you question. Internal configuration files are stored based on os on following locations: https://help.skipper18.com/expert-usage/reference-manual/internal-configurations
In case of OSX it's necessary to remove all plist files (and to be sure whole directory)
~/Library/Preferences/com.inventic s.r.o.Skipper
and restart computer (or log out/log in) because of plist file cache in OSX.