Upstream kernels rely on EDID data on the HDMI connection to determine the resolutions available. So one of the following applies:
a) TV has bad EDID data
b) TV has bad HDMI sockets
b) HDMI cable has a problem
c) WP2 box has an HDMI hardware problem
The AMLGX image shows 1080p/4K resolutions fine on my WP2 box so I'm confident there's no software problem. You can try forcing the kernel DRM layer to output at 1080p with "video=HDMI-A-1:1920x1080M@60" in kernel boot params, but that's not a proper solution since you'll be forced to play everything at 60Hz (which doesn't give great results).
To prove whether the box, TV, or cables are at fault .. connect it to another TV, use a different socket, HDMI cable, etc.
NB: If the TV shows "DVI" I'd start with using a different HDMI socket.