Cannot sync on iPhone


I am on Scrivener for mac 3.1.5 running on Mac 11.14.6 and I use the syncing with dropbox on an iPad pro, where I have Scrivenr for iOS.
At last I have a new iPhone running the last iOS 13 so I went on downloading Scrivener, which works fine, but I cannot sync the documents. When I try to sync I get the message “Syncing with Dropbox” for a few seconds and then the screen goes to the iPhone home screen.
I tried deleting and reinstalling Scrivener and Dropbox on the iPhone but to no avail.
The dropbox on iPhone seems working since I can see the Scrivener folder with the projects in it.
What can I do?

Thank you in advance.

Addendum on my previous post.

I erased my Dropbox folder, where I had 48 projects, and started adding them one by one, syncing each time the iPhone.
So far I learned that the sync works only if there are no more than 9 projects in the Dropobox folder.

It seems this problem is extended to other users. I hope the tech team is aware of this and find a solution.

There is a long thread on this elsewhere.
L&L are well aware of the problem but there is no systematic, consistent conditions that cause the problem. Some have problems with new devices, others with old devices. Some have problems with specific projects, with large or small projects, or with one specific project. But if the same problematic project is synced with another device it works.

The only thing that is common for all is that they run iOS 13. Devices running iOS 12 don’t have any problems.

About many projects… I have a subfolder in my Scrivener Projects folder and only sync that subfolder with my iDevices. I seldom have more than 3-4 projects that I am actively working on and that I need in the sync folder.

Thank you for your input. I realised there are many users having issues. I thought that maybe 9 was the key number for developers dept. to unravel the ravel. For now I’ll scale down my sync folder. Hope an update will fix this soon.
I moved back to iPhone just for Scrivener --and for the photos.