I am having the same issue now for https://dietpi.com/apt/dists/bookworm/main/binary-amd64/Packages.xz.
Unexpected size (2492 != 2552) Mirror sync in progress? [IP: 188.114.97.0 443]
Release file created at: Thu, 21 Nov 2024 19:11:21 +0000
That is a very recent update. Could it indeed still be updating on all mirrors?
I saw the same issue being resolved in July as well:
https://dietpi.com/forum/t/rpi-4-unexpected-filesize-error-while-installing-progs-update/20716/4