This may help -- Explanation of how to use the "Devices" and "Duplicate ID's" option for Inventory, and how they work.
Generally speaking, "ghosting" (if we're talking "cloning) OS'es is a bad idea, as all manner of unique ID's get cloned along with it.
As far as EPM is concerned, it *IS* possible, but people tend to forget to remove the unique ID.
I'm a bit head-scratching at the fact that "a device that HAS been seen by Ivanti EPM before won't see PXE" ... that sounds like there's something else awry (since it's really a simple "Hey - here's my MAC address..." and all the Core has to do is to check against that MAC).
What you COULD do, is turn on "store inventory scans" on (it's an advanced option for the Inventory service HERE):
That'll allow you to see whether the relevant mini-scan ever makes it to the Core. You MAY need to do some wiresharking though to see if *ANY* comms make it to the Core in the first place though.
You can pick up a big of Provisioning type troubleshooting info from here -- [Tech Brief On-Demand Webinar 2016] Provisionin... | Ivanti User Community -- where I cover a few things as part of a webinar I did on Provisioning a while ago (not much has changed since then, so you can use the info there - with basic www-service info around slides 11 onward) . The visual explanation of the way the Provisioning boot process works should help you (and help you Wireshark-trace problems).
Also there's a dedicated troubleshooting section (slide 50 onward) that may be of use.
If need be, this is something that support can help you troubleshoot, but it's not normal behaviour.
I suspect you will be wiresharking a bit to find out for certain where communications DO go and what's provided / not provided ... based on THAT, you can then hopefully figure out what's logically happening with the devices that already exist in EPM when they're being attempted to be re-imaged.