I have a GXV3350 that has been powered over POE. I’ve had no problems with it until today and now have to power the phone through the electrical adapter. I’ve tried moving the phone to other rooms/offices with other working POE phones and swapping them out, and the GXV3350 still doesn’t work unless powered by the electrical adapter.
I suppose the possibility exists that the phone’s PoE function is defective. It is rare as I can only recall two examples over the past 10 years or so.
If the phone is within its warranty period, contact your reseller for assistance in getting a replacement. If you bought this off of Amazon or other on-line platform, then contact them as GS only offers warranty coverage to those devices sold by approved resellers and approved on-line retailers.