I'm running Acrobat DC as part of Creative Cloud (CC) on several Macs. I use the sync feature to sync Acrobat preferences between all of these computers. I especially rely on the Acrobat preferences being sync'd for things like signatures and custom toolbars arrangement. I recently added two new computers, a MBP and an iMac Pro. When I installed CC and Acrobat DC on the MBP it worked fine. But on the iMac Pro Acrobat preferences sync is broken. The following steps illustrate the problem:

1) Reboot the system to start from a clean state. Make sure no applications or documents are open. See screenshots 1-3 for specific versions of Creative Cloud and Acrobat Pro DC.

2) Launch Acrobat Pro DC from Creative Cloud

3) Open Acrobat preferences, Adobe Online Services section (screenshot 4). Note "Sync preferences across devices and document services" is unchecked

4) Check "Sync preferences across devices and document services" (screenshot 5)

5) Click OK to close preferences. Try to reopen preferences to see if the preference change was successful and an error dialog is displayed (screenshot 6). The error message refers to another PDF document but no PDFs are open.

6) Quit Acrobat and try to uninstall and reinstall from CC (screenshots 7-9)

7) Reopen Acrobat and try to open preferences. Same error dialog (screenshot 10)

8) Reboot and reopen Acrobat again. Open preferences. "Sync preferences across devices and document services" option is now grayed out (screenshot 11)

9) Close preferences and reopen. Now the "Sync preferences across devices and document services" option is checked, although I didn't check it. (screenshot 12)

10) Quit Acrobat and relaunch. Open preferences. "Sync preferences across devices and document services" option is now grayed out again, but this time its checked (screenshot 13)

11) Close preferences and try to reopen. Now the error dialog is back (screenshot 14).

12) Quit and relaunch acrobat and open preferences - same error dialog.

13) Reboot and reopen Acrobat again. Open preferences. "Sync preferences across devices and document services" option is now unchecked and grayed out again (screenshot 15
)

14) Close preferences and reopen. Again, the "Sync preferences across devices and document services" option is checked, although I didn't check it. (Screenshot 16)

15) Quit Acrobat and relaunch. Open preferences. "Sync preferences across devices and document services" option is now grayed out again, but this time its checked (screenshot 17)

16) Close preferences and try to reopen. Now the same error dialog from steps 5, 7, and 12 above is back.

At this point steps 13-16 repeat in a loop. If I uninstall Acrobat the process goes back to step 6 and repeats from there.