Issues with Updating my SYNC3 MY2018 from Version 3.3 to 3.4 (SIGN_ERR01)

Since you have no Syn3 Updater lof file it is difficult to guess what is going on, but you are obviously trying to update the maps also, as the Sync OS would not give this code.

Have you performed a master reset then performing the update?
Try updating the Sync version to 3.3.19052 and see if this works. You will only need the one file, nothing else.