From what you reported, it looks like "Dnn01-000005-delta.vmdk" has an issue. This is the snapshot following 000003 in the chain. Please extract/copy the first 167936 bytes (164 kB) which contain the metadata from "Dnn01-000005-delta.vmdk" using e.g. dd and attach the resulting file (compressed/zipped) to your next post. I cannot promise anything, but maybe there's a chance to repair the metadata if this is corrupted.
... but snapshot #4,5,6,7 has IDENTICAL CID...
The reason the the CID and the parentCID being the same is that the vmdk has not been modified after it was created.
... the snapshot delta file's CID reference chain are rather odd ...
That's ok. When a snapshot is created, the first free number is used. If - for example - you have a disk with 5 snapshots 000001...000005 and you delete snapshot 000004, then next new snapshot will become 000004 (not 000006).
André