This is not actually part of the upgrade. After every upgrade, deferred tasks that failed before the upgrade at any time during a previous version are attempted again in case those tasks were fixed.
This error is due to a deferred task that failed while deleting old edits but managed to successfully deleted those edits already anyway. When reattempting, the edits are already gone and a database error occurs due to the missing IDs. This is due to a bug in the task where it trusts the data to exist when sending it to the delete manager, even though it should not make that assumption. This is a rare situation, and it will be fixed in the next build. The bug has existed, leaving open the potential for errors like this, since 4.0.0 RC 1 in 2014.
Note that each task is only attempted once and if it still fails, reloading the page simply bypasses it.