Using iOS devices and Field Maps 26.1.1, we have been unable to sync edits made offline. The errors are "Invalid JSON: The supplied JSON could not be parsed" which is also the general extent of the information we get from verbose logs.
Verbose logs are generally:
Preparing to sync 1 geodatabase
Sync geodatabase: Failed: "Job error 21 Invalid JSON. The supplied JSON could not be parsed."
Layer result: Sync failed. Name: ..... The supplied JSON could not be parsed.
Table result: Sync failed. ... The supplied JSON could not be parsed.
I wish the verbose logs included the JSON!