Syncthing v0.11 does not support synchronizing with older versions (v0.10 or older). Syncthing v0.11 will rehash all files on first startup. Syncthing v0.11 requires updates to other programs it integrates with. For details see the project release notes page at: https://forum.syncthing.net/t/syncthing-v0-11-0-release-notes/2426