Error 503. Service Unavailable on several pages + Scan failed

My site gives the Error 503 onseveral pages:
– Site Health Status
– Wordfence tools -> Diagnostic

And on Wordfence’s Scan page it says:

Scan Failed

The scan has failed to start. This is often because the site either cannot make outbound requests or is blocked from connecting to itself. Click here for steps you can try.

This is specifically the vulnerability scan.

Since I can’t access the Diagnostics page, I can’t use this option (from here):
Try starting scans remotely
Try enabling the option at the bottom of the Diagnostics tab on the Wordfence Tools page titled “Start all scans remotely”. Check the box, save and then try another scan. If it does not fix the problem, keep reading.

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