Commit 5bca7d8 changed the behavior of tombstoned replicas such that they now retain RaftConsensus instances despite being in the TOMBSTONED state. This means that some additional consensus-related state is included in their tablet report entries when a full tablet report is sent to the master. The master evaluates this consensus-related state when considering whether an evicted replica should be deleted, but it does not consider the TOMBSTONED state. As a result, the master notices that these tombstones replicas have been evicted, and asks the hosting tserver to delete them again. This will happen any time there is a tablet report.
This needs to be fixed, whether by excluding tombstone consensus state from tablet reports, or by changing the master to consider the tablet's overall state when deciding whether to delete it.
When observed on a live cluster, it was further observed that the tablet deletion requests were rather expensive. It appears that a DeleteTablet RPC on a tombstone is not a no-op; it always flushes the superblock twice, which generates two fsyncs. This should also be addressed.