“Looks like there is something wrong” error

Howdy,
I’ve been trying to make changes to the above linked website but I keep getting an error message saying, “Looks like something’s gone wrong. Wait a couple seconds, and then try again.” the website and wp-admin then becomes inaccessible for a couple of hours sometimes up to a day.
I have changed the theme to a default one (Twenty Seventeen) but I still couldn’t make changes.
I have also deactivated all plugins but the error persisted.
I contacted the hosting company and they informed me that they detected a mod_sec triggered on my site (Blind SQL Injection Attack) and they white-listed it.
The problem actually still persisted and I contacted them again. This time, I was informed that they found 406 and 401 on the logs as well and they whitelisted again.
Unfortunately, this problem still persisted.
I should mention that the site was hacked into(attempted actually) and I installed Last pass and Sucuri plugin thereafter.
I also activated the ssl certificate. How can I fix this issue?
Thanks a lot for what you do here.

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