Recently, I encountered this problems twice.
First on a Debian server, I initially cannot access WebUI. After pkill and restart btsync, accessing WebUI prompt dialogue of creating identity, and obviously all sync settings were gone. I had to switch to configuration file instead of WebUI on this Debian server just in case of losing folder keys.
Today, I received the notice of upgrading to 2.3.3 on a Mac. After upgrading, only one item was left in sync list. It's lucky that I can add all folders back using the keys in configuration file on my Debian server.
But I think developers should take a look at the stability of sync list. At least, some functions like backup/restore sync list should be considered.