It is finicky! There are multiple components outside of 1Password control when you are using Dropbox, iCloud, or WiFi sync.
We do our best to find, troubleshoot, workaround these issues. We have built an entire Troubleshooting and Diagnostics utility just for that: https://support.1password.com/diagnostics/
For the majority of users sync with third-party services works well. However, there cases when it gets finicky.
I don't use any third-party services. I use what 1Pw calls "Folder" sync, as it's the only non-cloud method available. 1Pw on Mac #1 saves a binary file to disk, and 1Pw on Mac #2 loads that file from disk. There's no components here out of 1Pw's control. Sometimes, 1Pw simply doesn't write the file on Mac #1, as I can tell by the modification timestamp.
I ran 1PasswordTroubleshooting.app, and sent in the 400KB report it generated. The response I got from tech support mentioned nothing about what might have been found in that file (or what they expected to find, which could prevent data from getting from the application to the filesystem). They simply gave the usual spiel about restarting/upgrading.