Did you check the PXE representative of the old core is uninstalled? Generally the PXE is installed on a specific PC. From 2016.3 and above, PXE can be depolyed by self elect.
Please make sure in the same subnet, there is only 1 pxe representative running.
So i did remove the PXE from the old core, If you look at the old core under configuration and PXE representatives, its blank. Now if i look at the new core under PXE reps it shows the new core.
is there something that the new core would look at that would maybe make it look at the wrong core, espoecially if some settings have been copied over from the old core?