Unable to save changes ERR_CONNECTION_RESET

Hello!

I’m having some major problems with my site.

Basically when I try to save a modification or change on the site it loads a bit and then Chrome gives an ERR_CONNECTION_RESET message (I tried with Firefox too, same thing). If not this, then WP will give an error message, for example when I upload an image it will say “HTTP error”.
I tried disabling all plugins and themes, but the problem remained. Also tried a “netsh winsock reset catalog” in cmd from another post which worked for like one save. For the next one the problem came back. So every time I wanted to save something I had to reset catalog and restart my pc. Which is not very practical. Since then, I also bought a new pc, so that cannot be the problem either.

Interesting thing is that other users who edit the site did not have the problem like I did.

So I feel like it’s not WP, not the computer, not the themes and plugins, but maybe my internet?

I’m hoping someone smart will be able to help.
Thank you in advance!

The page I need help with: [log in to see the link]