Observed in 4.7.5 in a clustered setup that has users log in with multiple resources, where only one resource sends initial presence.

The system-clustering-data-consistency-check.jsp shows for some resources this warning:

User sessions cache is missing entries that are present in the user cache.

The missing entries are all entries that have sent initial presence (which may be a coincidence). In the example that I analyzed, 11 sessions (out of approximately 200 sessions in total) were in this inconsistent state.