I have noticed that I get multiple sync failures after doing log dives (90 minutes and greater). It appears the FIT file gets to a size where a timeout between the Descent and Garmin Connect Mobile becomes more likely. This happens even when the Descent is less than a metre from my iPhone.
I'm sorry the image is so small. These fora make it impossible to upload a image and keep its size. You can at least see how many times sync has failed.
Here are the errors from the sync report which are common across all the failed syncs for long dives. Eventually, it will sync but it can take an hour of trying.
[FONT=courier new]UPLOADS
File Type Filename Size (bytes) Status
-------------------------------------------------------------------------------------------------
FIT_TYPE_4 1-3966683484ble-FIT_TYPE_4-2859-31-893653287 245543 Error
FIT_TYPE_35 (null)79 Cancelled
FIT_TYPE_32 (null)2901 Cancelled
FIT_TYPE_32 (null)484 Cancelled
FIT_TYPE_32 (null)431 Cancelled
FIT_TYPE_32 (null)624 Cancelled
FIT_TYPE_32 (null)431 Cancelled
FIT_TYPE_32 (null)569 Cancelled
FIT_TYPE_32 (null)554 Cancelled
FIT_TYPE_32 (null)902 Cancelled
FIT_TYPE_32 (null)749 Cancelled
FIT_TYPE_32 (null)554 Cancelled
FIT_TYPE_44 (null)335 Cancelled
FIT_TYPE_41 (null)14789 Cancelled
DOWNLOAD DEVICE FILE TYPES
File Type
-------------------------------------------------------------------------------------------------
DOWNLOADS
File Type Download ID Size (bytes)
-------------------------------------------------------------------------------------------------
ERROR DETAILS
Error Domain=GCMSyncErrorDomain Code=2 "Device connection error" UserInfo={SyncErrorReason=File UL: Failed to receive file from device, NSLocalizedDescription=Device connection error, NSUnderlyingError=0x1c4a5f3e0 {Error Domain=GarminDeviceSync.FileTransferErrorDomain Code=16 "(null)" UserInfo={GarminDeviceMessageError.ErrorReasonKey=Timed out waiting for file data request.}}}[/FONT]