Hi,
you may need to recalculate assignment of users to workflow workitems representing emails.
Please check in SWIA tcode if those workitems have proper agents(users)assigned.
Afterwards it may be needed to recalculate assignments.
I am not aware of any standard report for this as I am using custom one.
You can also refresh org str buffer.
Please check if job HRBCI_ATTRIBUTES_BUFFER_UPDATE if properly running.