Ok it is attached. Since you said you have some programming experience, imo you can take a quick look at the file and perhaps will be able to see how I added those tabs to the button array. This way you can add to it in the future if you want to add more tabs. That file will only work with the arcade installed as it inserted those hook configs in the settings table of your database to use that file & function.
Use your ftp platform (Cpanel, Filezilla, etc.) to upload the file to your Sources folder replacing the original arcade hooks file. Then uninstall and delete those 2 modifications.
This does not fix your issue and I have to get up for work in 3 hours so we will have to continue this tomorrow evening. In the meantime I suggest using trial and error to figure out what is causing the issue. Disable every block, uninstall every mod (except the arcade) including the portal until it works. Although I just tested it on a local installation with Simple Portal and a few other mods installed and it works without issue.