From the sounds of it, it is likely that you may need to change VPN providers as the one you are using is being blocked by our DDoS filter.
I have the same issue with SurfShark and only with this site.
I am not going to change VPN subscription just for your site...
I bought a 2 year suscription and all other sites including torrent sites work normally
This should be excluded on GT site ends.
EDIT: disabling SSL in my profile "solves" the issue. But it more of a workaround than a solution. Can't this be fixed on GT tracker end?