Any suggestions on this? I fear that not being able to clear my wpforo cache is causing major problems, all the while you are not able to debug the given problem for me (posting issues, certain users unable to reply to certain topics without any clear reason).

We don't find such an issue on our test websites. This is something specific on your website. If you can send use the duplicator plugin and send us the copy of your website we may check and provide some solution. 

Is there any other way to clear all wpforo cache for me not being able to access wpforo dashboard? And will you be able to make super admins able to access it?

Yes, there is a way to clear the caches via FTP. You'll need to delete the files from the /wp-content/uploads/wpforo/cache/ folder. 

However, please never delete exactly the folders, just the files from the folders. 

And don't delete the following two files:

• index.html 
• .htaccess 

Is there any other way to clear all wpforo cache for me not being able to access wpforo dashboard? And will you be able to make super admins able to access it?