Network type keep changing on it's own


I have a. DVR-9006UVD-BK

Recently I’ve had a problem with the Network Type changing to PPPOE on it’s own. Not sure what’s causing it to loose it’s setting after certain periods of time. It usually keeps it for a few weeks then I find I can’t reach the DVR remotely. I access locally and find the Network Type has changed to PPPOE… Any ideas on this problem.

Thanks Tom