I have been reading through all previous posts that I could find, on any issues related to problems with downloading areas for offline use on Collector (not Collector Classic).
In the few cases I have experienced recently, there are no copies of layers in the same webmap, or domain names that coincide with field names in any of the present layers (as discussed here and here). All layers are shared at organization and/or group level, with syncing enabled and offline mode enabled too for the webmap.
When trying to download an offline area (Area 1), it simply stops soon after starting and shows a blank page with a message "No maps to display" or similar. When re-trying, it will attempt to download 'Area 2' but the result is the same.
I have tried to find the log through Collector developer options, but the only thing I can see is 'Placeholder' which does nothing when selected.
The webmap is created from 3x Feature Layer (Hosted). One was created in ArcMap and based on a File Geodatabase and the other two are shapefiles that have been 'dragged' in.
This works fine on Collector Classic (and it has worked ok with Field Maps too), but the 'new' Collector (v 20.2.2) has very frequent issues with offline area download, even though the type of WebMap we create always follows the same structure.
Despite all layers being shared at organisation and/or group level, I have found that the error is more likely to happen when the user who downloads it is not the same as the user who created the webmap, even though both have equal permissions on AGOL.
Sorry for creating a new post - again after reading through other posts I found no solution to my case and I hope I can find some support here. I'm happy to provide any more information that might be useful to understand the problem.