Maybe contact the Mirror provider rather then the Kali team as these seems to be two different entities?

Could be also just a local network setup issue for https://forums.kali.org/ (Just because other services works might not proof there is none other issue)?

This mirror is working reliable, as far as I can see from our monitoring.

I tried, both IPv4 and IPv6, works for me:

wget -4 http://mirror1.sox.rs/kali/kali/pool/main/libs/libsdl2/libsdl2-classic_2.32.10+dfsg-4_amd64.deb
# works!
wget -6 http://mirror1.sox.rs/kali/kali/pool/main/libs/libsdl2/libsdl2-classic_2.32.10+dfsg-4_amd64.deb
# works!

Also, I'd think that connect (101: Network is unreachable) indicates a network issue on your machine, it's not a HTTP error code from the mirror.

In doubt, try to use another mirror. Edit your file /etc/apt/sources.list, and replace http://http.kali.org/kali with http://kali.download/kali, then try again. Tell us how it goes!

I commented the sox mirror and the process continued successfully, by using other mirrors and the main one , i'll try contacting mirror provider and feedback

Sometimes mirrors setup geo-blocking on their http server, eg. they block some countries, maybe that's what happened here?

This is happening to me too...

Get:1 http://kali.download/kali kali-rolling InRelease [34.0 kB]
Get:2 http://kali.download/kali kali-rolling/main amd64 Packages [20.9 MB]
Get:3 http://kali.download/kali kali-rolling/main amd64 Contents (deb) [52.3 MB]
Get:3 http://kali.download/kali kali-rolling/main amd64 Contents (deb) [52.3 MB]
Get:3 http://kali.download/kali kali-rolling/main amd64 Contents (deb) [52.3 MB]
Get:3 http://kali.download/kali kali-rolling/main amd64 Contents (deb) [52.3 MB]
Get:3 http://kali.download/kali kali-rolling/main amd64 Contents (deb) [52.3 MB]
Get:3 http://kali.download/kali kali-rolling/main amd64 Contents (deb) [52.3 MB]
Get:3 http://kali.download/kali kali-rolling/main amd64 Contents (deb) [52.3 MB]
Ign:3 http://kali.download/kali kali-rolling/main amd64 Contents (deb)
Err:3 http://http.kali.org/kali kali-rolling/main amd64 Contents (deb)
File has unexpected size (52315180 != 52314457). Mirror sync in progress? [IP: 104.17.254.239 80]
Err:3 http://http.kali.org/kali kali-rolling/main amd64 Contents (deb)
File has unexpected size (52315180 != 52314457). Mirror sync in progress? [IP: 104.17.254.239 80]
404 Not Found [IP: 54.39.128.230 80]
Hit:10 https://dl.google.com/linux/chrome/deb stable InRelease
Error: Failed to fetch http://http.kali.org/kali/dists/kali-rolling/main/Contents-amd64 404 Not Found [IP: 54.39.128.230 80]
Error: Some index files failed to download. They have been ignored, or old ones used instead.

Trying to update without using a VPN, and I'm in the USA.

@Jess Up Completely different thing and unrelated to this one.

Ok, Thank you.

I'll make a new thread for my issue.

I;m closing this one, as it was about the sox.rs mirror specifically.

Sox team has responded that they faced dozen of rsync attempts from egypt and they had to put ACL upon it

Once investigation the issue is complete,they will feedback