Why does Safari keep changing sites in my my favourites bar to previous versions

I spent over an hour last week editing my bookmarks in Safari, since I had begun to find that, when I added new bookmarks, they would disappear within hours or the next day. When I went to edit I found there was a list of maybe 30 Bookmarks Bars, many of which were identical but some of which had some differences. I decided to delete them all and rebuild a new Favourites bar from scratch. That worked OK for a few days and was still OK this morning. Then I went out for a couple of hours and now the favourites bar has reverted to the bookmarks bar I had before I made the wholesale edit. When I went to re-edit the bookmarks, there was once again an endless lists of Bookmark bars and the favourites bar was the same as my old bookmarks bar. The new favourites bar that I had taken ages to create has completely disappeared from the list.

I assume this is an iCloud syncing issue. However, although I have managed to find a lot of other people suffering the same issue in forums, I have not yet been able to track down a solution.

This is making my life a nightmare. Please can someone help me.