As mentioned before, I think these are temporary files from the migration that can be deleted. But as others or me can only guess on the files maybe it is best if you open a support ticket so that support staff can check this directly on your server. They will be able to definitely tell from where these files come, why they are there and what to do with them.
Question How to get support directly from Plesk? Answer Lease-type Plesk licenses purchased directly from Plesk running on supported Plesk version include full free support. Perpetual-type license...
support.plesk.com