I installed the 15.39 update and at first saw no difference. Digging a little further, however, I was able to get things resolved with this version.
In recent prior builds, I would get the error 0xE0000007 and it would be associated with the notebook name (Household, Reference, etc.). I had two of my nine notebooks erroring out. With this new build, I noticed the error code now showed the sections that
were a problem. Interesting observation 1: it was some old sections where the problem was occurring, not the ones with recent notes.
Using the new information, I created new sections in the notebook for each of the problematic sections, copied all the pages from the problematic sections to those new ones and then let the sync do its thing. The new sections with copied content synced correctly.
Interesting observation 2: I was getting ready to delete the old sections as the last step in the process, but after the new sections synced, the olds ones stopped erroring too. Go figure. Deleted them anyway for good measure.
After all that, everything is now syncing correctly. I went to my iPad and with a quick refresh, those started working as well. It's not quite a perfect fix, but it got the job done.