My guess is that when your sync fails repeatedly it often means that your sync files (in the hidden AppData folder) have been corrupted in some way. The only way to avoid starting over again is to backup these system files each time that you backup your tree. Then if you have a failure, you can fall back to something that was working.
In the latest update, they finally updated the built-in backup method so that it didn't break the link from FTM to AMT. I don't know if they also include the files from AppData with the backup. I've not tested that myself.
Not to discourage you both from trying to fix your broken syncs on your own. It may be possible to do something yet on your end, but I have no advice for that. My advice is for when you are up and sync'ing again that you backup frequently (and always after each successful sync)--and that you sync frequently as well to minimize the loss of work when there is a failure.
PS. Paul, it's generally bad form to include surnames with your postings that don't relate to those surnames. People searching for those names may find this post and be annoyed that it has nothing to do with the surname they're researching.