Your TV is probably the same in needing to use HDMI 2 or 3  with the 'enhanced' setting to get 4K HDR  @60hz input.   I picked the 900E mostly because rtngs.com said it was brighter (I'm not a movie purist - it's in a room with a lot of windows...) and it has good local dimming.   But yes you should have to look pretty closely to see any difference.   Note that the picture setting adjustments are for your selected port or the default so they stick to the input and can be set differently (wish you could do that with audio).   I had trouble with the TV Amazon app stuttering on 4k input until the last update and it still struggles a bit where it plays perfectly on the X1 app.

I don't know much about HiSense TV's but a quick google search found some youtube videos about having to update at least some models of the TV to enable HDR.  Have you looked into that?  It may also make a difference if you are connecting to the TV or the receiver.  If you go through the receiver first it has to be able to handle the 10-bit color of HDR video.

Getting Pink Screen on most on Demand HDR content except tv channels. Using a HiSense UHD 55" TV with an ONKYO Dolby Atmos Receiver. Switching HDMI cables is not making a difference. It mainly shows up in HDR Theater Picture mode; Standard and Vivid are fine when viewing regular TV.

Plz advise.

But you said the receiver was upscaling and the X1 was set to send 1080.   You might also try connecting directly to the TV until you get the right settings for the picture.

If you want HDR you probably want 3840x2160@60Hz  all the way through.

TV shows 3840x2160 as current resolution 

Setting back to 4K 2160 connected to Receiver. See pics. Even if connected to TV the same result. The tv automatically upscales everything even if it’s 480p.

Box Setting TV UnknownStandard HDRHDR Theater Pink Screen

Don't think the pics posted right.   If you use the youtube app with 'stats for nerds' displaying you should be able to see if you are getting 4k from the source through ( the 'current' resolution numbers).   But, as per the point of this thread, the  X1 YouTube app doesn't send HDR so you'll need some other source to see if the 10-bit color is working.    The Amazon Video and Netflix apps should do that, but they don't have a way that I know of to see the details of what they are sending.  On my TV, I can tell HDR because if I go to the picture adjustment menu it displays 'HDR' but other TV types will be different.

Have you made the 'enhanced' setting here? 

https://gregglestech.com/2018/04/25/hisense-4k-tv-how-to-enable-hdr/

Also, older HDMI cables might not handle the 18Ghz data rate, although it would be unusual for a short run.

Will check YouTube app later. Amazon and Netflix give me HDR Pink screen.

Yes the HDMI Function is set to enhanced. The display shows 3840x2160 even on YouTube app with box set at 2160p 60fps. The pink screen still occurs with HDR Theater Mode. On the AppleTV all modes function properly with HDR 10 mode enabled. Using 4K cable from Amazon and one that came with the box stating high speed Ethernet.

I don't know what 'HDR theater mode' means.  Is that a TV setting?  Most TVs should auto-detect HDR and only a few xfinity sources are going to send it (certain videos on Amazon and Netflix).   Perhaps you are forcing 10 bit color when most videos are going to be 8 bit.    I think the Apple TV has an always-on HDR mode where it upconverts everything to make it work with that setting.   The X1 is only going to send HDR when the source video has it and it expects the TV to recognize and switch.  You could check this theory by starting something you know is HDR before switching the TV to HDR mode - like Amazon's The Man in the High Castle episodes.  But even that might not work if you have to manually switch the TV because I think the X1 will auto-detect capabilities.  Some devices actually have to have the cable removed and replugged or be power cycled to re-check the capabilites at the other end.

In any case it probably is not worth fighting that battle since your Apple TV probably has apps to play all of the content that you can get in HDR on the X1 anyway .  Just leave HDR off when watching xfinity - or find a setting that will auto-switch. 

One other possibility - maybe "HDR theater mode' forces Dolby Vision.   The XG1v4 will only output standard HDR10.