Sorry for providing incomplete information for your question.
When Replication package fails, the LastSyncTime parameter is not updated and, thus, all the records (records that were processed in the failed run and records that were not processed) will be processed again with the next package run. The LastSyncTime parameter is updated only in case if package succeeds. Each next package run processes all the records that were changed since the last package run (LastSyncTime value).
Please note, we have updated Skyvia yesterday. Now, if replication package fails, successfully processed records are not counted.
As for response time, we are doing our best to process requests as soon as possible.
Thank you for your patience and thank you for using Skyvia!