Hdr 10 and auto stopped working after last update, when is it's a 4k UHD TV

not all 4K television support HDR, what is the make and model of your TV?

I think we've found the issue, but it still resolves a fix on Microsoft's end. In the Sony TV settings Dynamic Range is set to "Auto".

When playing games, streaming content, watching regular Blu-Rays, and watching 4K UHD with HDR turned OFF the TV works perfectly with the "Auto" setting.

When playing 4K UHD with HDR turned on the Dynamic Range setting on the TV needs to be changed from "Auto" to "Limited". This resolved the issue.

But, if you leave "Limited" on for doing anything else the picture looks messed up.

It seems as if the Xbox One S isn't triggering HDR properly. If you go to the Reddit link you can see the information described in Update 5.

i have an older 4K tv with UHD, and when i set it to 10 bit with UHD on, i can clearly see the vibrancy and detail.

however, on the 4K test it shows the TV does not support movies and games at HDR 10, but supports 4K gaming @ 60Hz

theres other TVs which do show HDR 10 working with movies and games; however cheaper models will not give a full range and may just be a slight enhancement.

i would wait till 4KTVs standardize 10 Bit HDR and Dolby atmos, as theres very few TVs on the market now which truly show the potential of HDR.

I have the Xbox One S set to Auto and the TV set to Auto. I never mess with those settings and the Samsung Blu-Ray Player I used worked fine.

Right now I'm manually updating the TV settings to "Limited" when playing a 4K UHD with HDR. Whenever I do anything else I change the TV back to "Auto" and it works properly.

Do you think a firmware upgrade from Xbox could fix this?

you need hdr for 4k output

Actually, you don't.

Uhd and hdr are required for 4k output

You need UHD, in the sense that you need the TV to support 3840 x 2160 resolution, but you don't need HDR enabled to reach 4K. UHD 4K is the amount of screen resolution available measured in pixels, HDR is the ability of the TV or monitor to display more
natural colours.

Note that the Xbox One S can do HDR in games that support such a feature, but regardless of what resolution you set, all games max out at 1080P internally. If the display is 4K, it will remain in 4K, but games will only be upscaled. Only the Xbox One X
can play Enhanced titles in 4K natively.

You should be able to disable HDR, how you disable it depends entirely on your TV. Disabling HDR via the TV settings should not disable 4K screen resolution. Indeed, some Xbox One games do not support HDR, Fallout 4 on the One X can play in 4K for instance,
but it does not support (or indeed have an option for) HDR.

On my Sony Bravia Android based TV, I had to go to the main settings and enable HDR functionality. Even then, I had to set the HDR setting to 'Auto' on the HDMI port I have my console connected to. If you have HDR set to 'On' all of the time, non HDR games
will display the wrong colours, look oversaturated. With 'Auto' enabled, HDR will only operate when it detects an HDR supported game. This may not be a feature of your display however.

What make and model is your TV?