It is loading here, are you sure it's actually down?

I am getting the error below at both home and at work.

Get:8 http://ftp2.nluug.nl/os/Linux/distr/kali kali-rolling/contrib amd64 Contents (deb) [155 kB]
Ign:8 http://ftp2.nluug.nl/os/Linux/distr/kali kali-rolling/contrib amd64 Contents (deb)
Ign:4 http://http.kali.org/kali kali-rolling/main amd64 Contents (deb)
Ign:8 http://http.kali.org/kali kali-rolling/contrib amd64 Contents (deb)
Err:4 http://http.kali.org/kali kali-rolling/main amd64 Contents (deb)
File has unexpected size (41442477 != 41433921). Mirror sync in progress?

Ending with
E: Failed to fetch http://http.kali.org/kali/dists/kali-rolling/main/Contents-amd64 File has unexpected size (41442477 != 41433921). Mirror sync in progress? [IP: 145.220.21.40 80]
E: Some index files failed to download. They have been ignored, or old ones used instead.

A colleague told me this happens when the mirror is down so I assumed that's the problem, my apologies is it's another issue.

Typically when the message is "Mirror sync in progress?" it means that the mirror is in the middle of syncing, and not down. It could be that you are attempting to update at the same time(s) that the mirror happens to be syncing. Are you always attempting to sync at the same times? Can you give it a couple of hours and try again?

Definitely! I'll try again tomorrow. I tried it yesterday (about 30 hours ago) and today multiple times, colleague mentioned he had the same issue on Sunday.

Issue still ongoing, same message, different network, instance and time than yesterday.

Looks like it works again!

Okay, I'll close this, but we'll keep an eye on the mirror.