Cannot install mods to an existing game on headless Linux server [0.17.79]

[asg0451]

I have a Factorio instance running headless on a Ubuntu 16.04 server. I want to add mods to an existing save there but cannot manage to do it. the mod-list.json (attached) file updates with each mod added, but the mods are never loaded into the game.

Factorio lives in /opt/factorio. This is the invocation I use (working dir = /opt/factorio):
./bin/x64/factorio --start-server-load-latest --console-log factorio.log --server-settings data/server-settings.json --server-adminlist data/server-adminlist --mod-directory mods --verbose

What happens - nothing. The mod-list.json file is updated, but the mods are not available in the game. They are also not mentioned in the logs.

Furthermore, if i try and install mods locally and connect to the server, i see this (fact-serv-sync-conf.png), and if i click 'Synchronize', I'm brought to this screen (fact-serv-sync-cant.png), and i cannot click the 'keep enabled' checkbox. All i can do is hit confirm, which restarts my local game without the mod.

More version info:
]$ ./bin/x64/factorio --version
Version: 0.17.79 (build 47865, linux64, headless)
Binary version: 64
Map input version: 0.15.0-0
Map output version: 0.17.79-0


Any help would be appreciated, thanks!

attachments:
mods.zip - my mods folder in /opt/factorio/mods
server-settings.json - server settings file
factorio-current.log - log file
june.zip - the save game
fact-serv-sync-*.png - screenshots described above