This is observed in one of our env:
1. A MR Job was running which has created some temporary files and was writing to them.
2. Snapshot was taken
3. And Job was killed and temporary files were deleted.
4. Namenode restarted.
5. After restart Namenode was in safemode waiting for blocks
1. Since the snapshot taken also includes the temporary files which were open, and later original files are deleted.
2. UnderConstruction blocks count was taken from leases. not considered the UC blocks only inside snapshots
3. So safemode threshold count was more and NN did not come out of safemode