This is something I routinely see myself in multiplayer, and I (and many other RIOs I fly with) assumed it was just the actual AWG-9 modelling.
After looking through all the documentation I can find and testing in singleplayer, I can't get the repeated ghost contacts problem to show up when looking for it.
If it's caused by INS drift, it's an EXTREMELY aggressive drift to make the contact drift 10s or 100s of NMs between radar hits while the own A/C INS solution is only drifting maybe 1-2NMs.
It shouldn't be related to datalink either, as the contacts that are duplicating are radar contacts, not datalink contacts.