Not getting Dolby Vision/HDR from HBOMAX

I have the xi6 box for my 4k tv (LG). Normally I would use the LG apps to watch streaming but LG and HBOMAX don't have an agreement so i use the xfinity box. For several weeks now when i watch new HBOMAX movies that say HDR/dolby Vision it does not come through. The LG tv will say at the top that I am watching in HDR. I have reset the box and signed out/in several times with no change.  Any idea why this is happening?