In AF-20983, the primary hit invariant(lastWritten >= lastCommitted) and crashed. We determined that DSC doesn’t actually guarantee the invariant since the the Log Service commit point can advance before lastWritten is updated locally in the onCommit() handler.

The invariant holds in ASC because lastCommitted there is derived from the members' lastWritten values, and therefore cannot exceed the primary's own lastWritten. 

In DSC, however, lastCommitted depends on Log Service acknowledgement (which can be read earlier than the onCommit() handler) and may temporarily advance beyond the primary's lastWritten. The action item from the AF is to downgrade the invariant to a warning and document that in DSC that lastWritten is not necessarily >= lastCommitted, including an explanation why.