It’s a common problem that affects all WDTV media players … it’s a HDMI (EDID) Handshake issue between the WDTV & your TV
You can try setting the WDTV resolution to AUTO and see if your TV displays 1080p while watching a movie … (press display button on your TV remote)
There’s been lot’s of posts over the years regarding the problem… (here’s just a few)
I did try this a while ago and seemed to work … but i keep forgetting to do the procedure (so i just change the setting)