DIsparity between developed and exported image

For those on this thread:

If you send the affected image to Camera Raw does Camera Raw render it correctly or the same as Lightroom Classic? 

I'm seeing the same bug and have reported it. Here's a workaround, but it only works moving forward. It won't fix images you've already processed.

When you go into the develop module to edit a new image, Zoom to 100% or higher then return to the Fit zoom setting. It appears that from then on, the Develop and Library views will match. At least, that's working for me.

Did you use the new Select Subject mask for this?

Please select a sample raw showing this problem, do Metadata > Save Metadata To File, upload the raw and its xmp sidecar to Google Drive, Dropbox or similar, and post the sharing link here. That will allow Adobe to confirm the issue and file a bug report (they generally don't pay attention without a reliable way to reproduce the problem).

You export in what color space and then view that JPEG where? 

It isn't unexpected that Library and Develop modules will differe visually since they use a completely different preview architecture. NOT to the degree you show, but it is important to recognize that the Develop module at 1:1 or greater zoom is the only accurate way to preview your image data and edits. 

Since you have some work to do, you might try going back a version. To go back to thelast version, use Creative Cloud application, next to the product you want to revert, click on... pick "other versions" any better? 

Other things to try if Adobe didn't mention them:

Try disabling GPU in the preferences (Preformance tab). Any better?
If not, recalibrate and build a new ICC display profile, the old one might be corrupted.
If you are using software/hardware for this task, be sure the software is set to build a matrix not LUT profile, Version 2 not Version 4 profile.
If turning OFF GPU works, it's a GPU bug and you need to contact the manufacturer or find out if there's an updated driver for it. 
Also see: https://helpx.adobe.com/photoshop/kb/acr-gpu-faq.html

The fact that library and develop don't appear the same, may be caused by a corrupt display color profile.

Even though calibrated, please try what happens when you use a default sRGB profile for the monitor.

- Does it affect all exported photos or just some?

Some

- If you enter the develop module again, do you still see it corrected?

Yes

- While in library, does the look match with the develop module?

No

- To which format did you export? You are probably aware that you need re-export after additional changes.

JPG (Yes very much aware) 🙂

- Is your screen calibrated?

Yes

Some questions:

- Does it affect all exported photos or just some?

- If you enter the develop module again, do you still see it corrected?

- While in library, does the look match with the develop module?

- To which format did you export? You are probably aware that you need re-export after additional changes.

- Is your screen calibrated?