There can be an error when you backed up your company file, css321. 

I read the thread and I agree with the recommended workarounds provided. I suggest reaching out to our Customer Support Agents to help you sort out the root cause of the Temp backup files since the issue persists. They can open an investigation for you so our engineers will be aware of it. 

Here's how to contact us:

1. Go to the Help icon and select QuickBooks Desktop Help (F1).
2. Click the Contact us link.
3. Enter your concern that QuickBooks creates a Temp backup file using Dropbox. 
4. Click Continue.
5. We provide options on how you'll want to connect with us. 

You can always reach out to me if you have further questions.