this is the 2nd time in less than a month :
/var/cache/dnf/updates-7exx87xxx825xx0d/packages/kernel-core-5.15.5-200.fc35_5.15.6-200.fc35.x86_64.drpm: md5 mismatch of result
/var/cache/dnf/updates-7exx87xxx825xx0d/packages/kernel-modules-5.15.5-200.fc35_5.15.6-200.fc35.x86_64.drpm: md5 mismatch of result
Some packages were not downloaded. Retrying.
Failed Delta RPMs increased 67.4 MB of updates to 105.5 MB (36.1% wasted)
dnf clean all
dnf update
dnf upgrade
Errors can occur with any download, at any time, and for many reasons. Dnf is smart enough to check the downloaded package and retry it until it gets a download that is acceptable. With delta rpms it will fail over to the full package as said by @vgaetera above.
It uses the same technique to switch to a different mirror site if it cannot get the requested package from the current mirror.