It's nice to hear from you again, @meganr.
I'd be glad to lend a hand with your automatic backup concern.
We haven't received any similar cases reported to us. To single this issue out, let's try resetting your automatic back up set up.
If the problem continues after trying this process, we’ll need to verify the data to help detect the cause of the error, then run rebuild to resolve it.
Here’s the article that details the steps to run the verify and rebuild utilities: Resolve data damage on your company file.
Once the rebuild completes, please verify the data again to ensure there aren’t any other issues in the company file.
If you’re still unable to back up the file automatically, I recommend getting in contact with our QuickBooks for Mac Technical Support Team to further investigate this issue.
Keep me posted how things turns out. I'll be around to help if there’s anything else you need while working in QuickBooks for Mac.