I use syncthing on 2 computers with a single to synchronize. When i installed syncthing on my samsung S5 and set the id device and share, my file was erased on the 2 computers
!!!
Just stating the result is not very useful if you want to understand what happened. For that you usually need to explain in as much detail as possible as to what you did, what folder types, were they empty or not, etc.
You probably pressed override changes button which pushed phones state to everyone else, which starts of empty, because it’s a send only folder by default.