If the connection to the remote server times out then the current sync run will finish and report a Failure or Partial Failure error.

Subsequent syncs will attempt to continue transferring the remaining files, omitting those files that have already completed successfully.

Much like the slow transfer times issues, if the transfer duration is longer than the connection timeout, then the next run could restart the transfer over from the beginning, causing an endless retry loop where the file never gets completely transferred to the remote server.

To resolve this issue, contact the administrator of the remote server and ask if they can configure a longer connection timeout duration or limit the file sizes of your files so that they can be fully transferred within the duration of the connection.