We just had a partner contact us to let us know that downloading maps for offline use is not currently working. In Field Maps designer I am getting a green check mark and there doesn't seem to be any errors showing up. The feature services have not been modified in quite some time. This is the error that is currently showing in the logs. I am also not able to download maps while in good cell signal and Wi-Fi turned on.
Are you using ArcGIS Online or Enterprise? For Enterprise maybe the account used to get the Esri basemaps for offline use ran out of credits?
@HannesVogel - ArcGIS Online
Just happened to us as well. I went into FM Designer and "updated" all our offline map areas, even though nothing has changed in the main map. This worked - offline areas now download correctly. Don't know why, but this worked.
Unfortunately, we do not have any predefined offline areas and everything on my end looks as it should. The partner has narrowed it down to 3 layers that seem to affect the offline ability. These are some screenshots of FM Designer on my end.
Can confirm that deleting all of the indexes on each layer that contained a hyphen solved the issue, however, the download is extremely slow.