Sort of... It seems to be a delay between deployment of the package indexes and the corresponding packages, either one being updated while the other is older will give the same "checksum or size mismatch".
I believe what you are seeing here is what I describe at the bottom of this comment: Owut: OpenWrt Upgrade Tool - #535 by efahl, i.e., you are in that rsync window where things are not fully available yet.
These same symptoms were being generated by the ASU server caching the package indexes, so that there was an artificial delay between their being updated on the downloads server and what the ASU image builders were seeing.
Quite probably just waiting a bit for the build results to be fully populated on the downloads server. (This might also depend on where you are on the planet, and how long it takes for your local CDN endpoints to get the new/consistent files.)
If this persists for more than 8-10 hours, I'd say something is broken upstream, so try again and let us know either way.