You may be able to bypass part of the issue here.
I managed to get things fully resynced despite the checksum errors causing the same issue.
It seems like because the checksums cause failed downloads it aborts saving the repodata folder. (SUSE please fix this too).
What you need to do is go to the folder where the repodata is meant to be, start the mirror operation and wait for it to download the repodata to a temporary folder.
When you’re sure it is no longer touching anything in the repodata folder (lsof) copy it to the correct location.
For me this was effectively:
rmt-cli mirror > /dev/null 2>&1 &
cd /usr/share/rmt/public/repo/SUSE/Updates/RES/7-LTSS/x86_64/update/
lsof +D .tmp_metadata/repodata/
# wait a bit for nothing to be accessing it
cp -R .tmp_metadata/repodata/ ./repodata
This is somewhat janky but appears to work fine.
Edit: Added the > /dev/null 2>&1 or that might get very hard to read in the CLI.