I have experienced issues with most if not all of the ones you have mentioned.
Where does the dashboard receive the information from? Does it get it from PFSense? Then it should be accurate since PFSense is accurate. Or does it go out beyond the PFSense and discover the network on its own?
I have done quite a bit of diagnosing myself and in each instant the PFSense & my Unifi Controller will display the same Hostname while the dashboard will show a different hostname.
Regarding the Single MAC with Multiple IP addresses, how is it possible for an IOT device on its own isolated VLAN, to receive an IP Address from a totally different VLAN (also isolated)? This even goes as far as the device submitting an unblock request, but when checking the back-end on which device actually made the unblock request, the logs showed it was a legitimate request but from a totally different IP address.