Issue with AJAX response and 403 permission errors - Trying existing recommendations but running low on options

I'm currently trying to trouble shoot an issue with getting "Invalid AJAX response" and "HTTP/1.1 403 forbidden return" errors in Grav admin. So far this has been seen on an existing website and also on a brand new Grav setup for testing (different domain, same shared hosting space).

So far I've been trying solutions found in related posts, including setting Remote Fetch to fopen and curl and Remote Verify Peer (SSL) to No (as mentioned here: /forum/support/invalid-ajax-response-t3948 and here: https://github.com/getgrav/grav-plugin-admin/issues/1626).

Currently trying to explore any other firewall or connection blocking reasons with my host provider as well but I'm currently running low on ideas. I started down another rabbit hole of checking OpenSSL and Curl versions for any miss match but no luck there either.

Nothing has changed recently that I'm aware to explain the sudden issue either. If anyone's experienced similar and any other solutions helped would be really appreciative to hear them. Cheers!

@SystemXIII, If you think this is a mishap of Admin, please create an issue at the repo of Admin. That's where the devs eat and sleep.

Thanks for the post and suggestion! I've created a related issue there too (https://github.com/getgrav/grav-plugin-admin/issues/2254)