It looks like there was an issue with the gpg key verification for the repository index generation.
As the console output mentioned it didn’t finish the export so the repo was expected to remain in the state it was before, so you’d see older packages in the index, but the newer packages might have already been dropped into the pool so a proper installation will generate checksum errors.
Hmm, I think the job does a sequence of operations and if an earlier one fails like in the noetic buster case (the removal before the replacement) it can end up with an empty repo. There’s new noetic packages on the way which means that the job’s already queued for a build. When the rebuild is complete for noetic buster it will rerun the sync.