When deleting a device with prevent rediscovery disabled, it's added to the blacklist .
UIM 23.4 CU2
This is working as designed As part of the deep clean process, we first add the device to blacklist, perform actions, then unblacklist the device at the end of the process.
In case, the "prevent rediscovery" is selected, then the device is left in the blacklist. You can verify the Delete Device Status from OC inventory.
We need to wait for the job status page to show Failed/Success.
If the status shows success you should not see the device in the blacklist table.