Fixed! You are correct - two different google accounts were being sync'd.
I have diarium on two different profiles on my phone (long story as to why), but I had intended to only log into the primary google account while using Diarium. The sync error occurred while using the second profile (different email address). I checked the other account's google drive, and the diarium database was backed up to that account. Ultimately, I removed it from profile #2, and now there is no issue.
There is no need to merge the two accounts because I had only done test entries as I checked the sync error. I deleted those entries.
Thank you for your help. This was 100% my error and had nothing to do with Diarium.