Some advice on edgebanding with HPL. Priming is indeed important, but you need to use the correct primer - otherwise you will see delamination over time. Using a PVA or contact solution primer will initially deliver good adhesion. However, PVA is not compatible with EVA hot melt, so you can expect the bond to weaken with time. Contact cement also has long term issues, as the plasticizers used in contact cement also attack EVA over time.
Jowat makes an actual EVA based HPL primer (148.50) that is easy to apply and gives the long term performance. Note: Make sure your primer brand matches your adhesive brand.
A few other tips. HPL is very temperature conductive, and rapidly cools hot melt glue. Preheating HPL strips(in a heat box or with hot air during application), and increasing EVA glue temperatures to 210C when running HPL will improve your adhesion. Also, if your edgebander has the ability to reverse the glue roller direction, this is helpful in extending the hot melt open time, and really boosts adhesion for HPL. I would only use the reverse direction when running HPL.
One last tip. Jowat now offers a special PUR granulate adhesive (608.00) that can be run in an EVA glue pot. This adhesive can be used when you have periodic PUR adhesive needs, and allows you to go back to EVA. It has extremely long gluepot stability, and doesn't thicken or cure quickly in the glue pot, like the old style PUR adhesives. With the PUR, you would not need to prime the HPL.