Hi, 

From the logs it seems that the live merge operation failed because of a volume that still found on the chain and didn't removed - 

2021-10-26 22:36:20,654+01 ERROR [org.ovirt.engine.core.bll.MergeStatusCommand] (EE-ManagedThreadFactory-commandCoordinator-Thread-10) [666e0f97-8b02-4b1e-80d4-2a640dd28d90] Failed to live merge. Top volume 069d1cc2-cd2d-4160-8ca0-657f6f57c168 is still in qemu chain [069d1cc2-cd2d-4160-8ca0-657f6f57c168, 751c65f5-868f-4b05-9986-e3f028fa1579, 2b1f324c-31a4-4db5-80fa-278e631a59bb, 4e8ea055-54bc-4a19-813c-79f6fe3e2db1]

And -

2021-10-26 22:36:20,664+01 ERROR [org.ovirt.engine.core.bll.MergeStatusCommand] (EE-ManagedThreadFactory-commandCoordinator-Thread-2) [666e0f97-8b02-4b1e-80d4-2a640dd28d90] Failed to live merge. Top volume 20640e9a-e8fc-48f6-af45-7c4e80729717 is still in qemu chain [625cf5c8-4cfb-4356-8bb7-e0103e01943b, ce345f57-b12b-463e-b5d0-bc4f71fa3624, 46f180de-d855-4cda-be39-0c766d6b9bec, 20640e9a-e8fc-48f6-af45-7c4e80729717, 1b668588-2533-4ab0-8775-5fab04ade133, e96fb224-be29-486b-9692-9959f7090bd5]

The logs suggest to retry to remove the snapshot again - 

2021-10-26 22:36:22,628+01 ERROR [org.ovirt.engine.core.bll.snapshots.RemoveSnapshotSingleDiskLiveCommand] (EE-ManagedThreadFactory-engineScheduled-Thread-31) [666e0f97-8b02-4b1e-80d4-2a640dd28d90] Merging of snapshot '679b1d4f-b36e-427a-8545-7ff7409a2e8a' images '4e8ea055-54bc-4a19-813c-79f6fe3e2db1'..'069d1cc2-cd2d-4160-8ca0-657f6f57c168' failed. Images have been marked illegal and can no longer be previewed or reverted to. Please retry Live Merge on the snapshot to complete the operation.

Can you try it?