Syncthing 1.2.0 and newer do not interoperate with 0.14.45 and older
Starting with version 1.2.0, Syncthing always uses large, variable-sized, blocks to index and transfer files larger than 256 MiB . Syncthing version 0.14.45 and older will initially appear to accept files scanned with large blocks, but will later panic and shut down during some internal file operations. Do NOT install those versions, or enable large blocks in older versions, in clusters with devices still on v0.14.45 or older, e.g. Debian Stretch servers using distribution-provided packages.