I noticed this on my app, but it is also reliably reproducible using the DBRoulette sample app. Using SDK 6.3, iOS 15.4.1 and an iPhone Pro 12.
If you link to a Dropbox account, then unlink (this step may not actually be required) and then shortly afterward attempt to link to the same Dropbox account, the link fails with a network error. If you then try to link again it works fine, and if you wait a few minutes it also works. Suspect it may be an issue with re-using a stale network connection?
The issue occurs specifically when control is passed back to the app and it attempts to retrieve the token.
While not a very serious issue, re-linking is something that is often performed when troubleshooting issues with connectivity.
I can't attach the full log snippet as it marks this thread as Spam for some reason, but the main entries are listed below:
[connection] nw_read_request_report [C6] Receive failed with error "Software caused connection abort"
Task <01053FC1-6F47-4A0E-8C3D-1E80465C2987>.<5> HTTP load failed, 37/0 bytes (error code: -1005 [1:53])
Task <01053FC1-6F47-4A0E-8C3D-1E80465C2987>.<5> finished with error [-1005] Error Domain=NSURLErrorDomain Code=-1005 "The network connection was lost." UserInfo={_kCFStreamErrorCodeKey=53, NSUnderlyingError=0x28225ca80 {Error Domain=kCFErrorDomainCFNetwork Code=-1005 "(null)" UserInfo={_kCFStreamErrorCodeKey=53, _kCFStreamErrorDomainKey=1}}, _NSURLErrorFailingURLSessionTaskErrorKey=LocalDataTask <01053FC1-6F47-4A0E-8C3D-1E80465C2987>.<5>, _NSURLErrorRelatedURLSessionTaskErrorKey=(
"LocalDataTask <01053FC1-6F47-4A0E-8C3D-1E80465C2987>.<5>"
), NSLocalizedDescription=The network connection was lost., NSErrorFailingURLStringKey=https://api.dropbox.com/oauth2/token, NSErrorFailingURLKey=https://api.dropbox.com/oauth2/token, _kCFStreamErrorDomainKey=1}
