Strange issue with some WP websites

Hello everyone,

i encountered two days ago a very strange issue.
Some of the websites i have with WP installation , began to be really really slow. Both in front end and in admin panel. It is slow to the point that they become non usable…
What i have tried so far:
Fully updated the websites with the issues both plugins and theme.
Cleared all caches.
Updated Cyberpanel.
Reinstalled Immunify AV (because for some reason i was getting a 404 when tried to open the immunify page)
I tried sudo apt update && sudo apt upgrade -y.

Yet nothing.

One strange issue i also found is that i cannot ping or use curl to wordpress.

failed to connect to wp

I literaly cannot find or isolate any reasons on why this is happening. On one of my websites the user just stopped receiving email from all the big providers (gmail, hotmail etc.)…

I would be gratefull if anyone could guide me on why this is happening and help me resolve this.

Thanks in advance,