I created a custom camera profile using Colorchecker Camera Calibration application which works perfectly in Lightroom desktop, and when synced to the cloud it works perfectly on lightroom.adobe.com for a few minutes, after which the browser based app says "This profile is missing". Note that I spent over 4 hours on a chat with Adobe support techs and even gave them access to my system, removed my mcat file, rebooted my mac, and did a complete clean reinstall of Lightroom CC.
Steps to reproduce:
1. Create a custom camera profile. I used ColorChecker Camera Calibration application. If needed I can provide the profile I am using. I have tried several different profiles with same result.
2. Import the profile into Lightroom CC.
3. Apply the profile to some photos.
4. Wait for sync to cloud.
5. Immediately go to lightroom.adobe.com and open the adjustment dialog for the photos with profile. In my case the correct custom profile was listed and it worked (in other words the correct color adjustments were made). I could change to a different profile and change back with no issues. I could also switch to a different photo and back and it was still fine.
6. Wait a few minutes and access the same photos again in lightroom.adobe.com (I did not even close the app, I simply switched to a different photo and back. My experience is that now I get a 'This profile is missing' error (attached). If I go to one of the other photos I previously tested then all show the same error and the colors are not what they should be if the profile was applied.
Note that I did absolutely nothing in between the profile being present and working correctly on lightroom.adobe.com and the profile being missing, except switch back and forth between images. And as noted, even that worked for a few minutes, but once the profile showed missing in one photo it showed missing in them all.
Also note that I went through this entire process three times while on the phone with Adobe tech support, the second time after having removed the .mcat file and rebooting my mac, and the third time after doing a complete reinstall of Lightroom CC.
I also tried two different browsers. Same result.
Lightroom desktop continues to have no problem with the custom profile.
Expected result: The profile should be synced to the cloud and should work correctly on lightroom.adobe.com, forever.
Actual result: Initially the profile does sync and work correctly on lightroom.adobe.com but after a few minutes it disappears, a 'This profile is missing' error appears under the profile name (which is still my custom profile name), and the photo is displayed with default profile.
A significant side effect of this failure of the custom profile in the cloud is that all photos with that profile that are publicly (or privately) shared on the web have the wrong profile used and look terrible.
The key fact here is that for a brief time the custom profile works fine on lightroom.adobe.com, proving there is nothing wrong with the profile itself (especially since it continues to work fine on Lightroom desktop).
Peter, I really appreciate your help, and of course your coworkers, on this issue over the last couple weeks. I look forward to a fix in a future update of Lightroom now that you have pinned down the cause. You are everything a support engineer should be, knowledgeable, respectful, helpful, and responsive.