Connection with server lost when using Unison over SSH

I have a file server running Raspbian and a workstation running Ubuntu MATE 16.04. I use Unison to keep my home directory in sync. I’ve set it up to use a SSH connection. The workstation runs Unison 2.48; the server has multiple versions (including 2.48). I’ve successfully propagated a couple of changes from the workstation to the server that way. Now I’ve changed a file on the server. Unison looks for changes and correctly suggests updating the local copy with the file from the server. However, when I click **Go**, I get the following error: Fatal error Lost connection with the server. Unison settings are as follows: # Unison preferences label = Home dir root = /home/me root = ssh://me@fileserver//srv/file/me sshargs = -C addversionno = true dontchmod = true perms = 0 path = Documents path = Pictures General configuration problems (missing Unison version on server, wrong path etc.) are unlikely as changes are being detected and I have synchronized data various times (always workstation to server). It’s just the server-to-workstation scenario that fails. I decided to “sacrifice” my edits to the new file and chose to replace the server version with the outdated local one. Surprisingly, that sync run completed successfully—everything works unless there are changes on the server side. What’s happening here?