I followed the instruction here:
To make an online-only file available to open in third-party applications:
1. Open your Dropbox folder in Finder.
2. Right-click the file you want to have available.
3. Click Make available offline.
4. The file will be downloaded within your Dropbox folder and can be opened through any third-party application.
Once an online-only file has been downloaded in Dropbox, you’ll see the cloud icon change to a green checkmark.
to make the problem file available offline. Was able to open in ios with material I created on iPad that wouldn’t previously sync.