I've got a long-running SeaBlock save, and this mod worked great in single player to expand the my island base efficiently while I was doing other things.

With all that success I decided to do a massive amount of expansion overnight, laying down a swath of new city blocks and leaving it to run as a headless task on my server. Sadly when I logged in in the morning nothing had really happened. I had another couple of tweaks in single player mode, as perhaps it was the wrong landfill type or something like that and over the course of a couple of hours it built me a couple of city blocks (things are slow in seablock)

I then reloaded the save in headless and it did nothing again over the course of 8 hours.

I thought maybe it's just loading in multiplayer mode, as noted here, but when I hosted on the same server, with the same settings, but left it in GUI mode it seems to carry on working more or less indefinately.

Screenshots below of the progress it made over the course of 10+ game hours headless and around 3hours muiltiplayer GUI mode:
Headless: https://1drv.ms/u/s!AjAaK-BVbphXkzyfX5FtS3Q4cklc?e=9FtFBa
GUI (note still more to build): https://1drv.ms/u/s!AjAaK-BVbphXkz1Ar7mg68opxoz9?e=uXuv3K

No idea why this happens, I don't know any reason it should behave differently on a headless server, I not even sure where I should begin looking for this issue.

Perhaps because there's no "player", so there's no player settings?

Well no the settings (aside from the new setting to update everything in a blueprint book at once) are runtime-global which means they are per save game, not per player. That's the thing I don't know of anything that would be diffrent on a dedicated server.

Fair enough! If it helps I've got the autosaves, and the logs of both headless and gui versions online here:

https://public.livedrive.com/portal/public-shares/mklefas/*_NzVlOTYzNWVkYjNhNGMxNWE4MmJhNjliNGQ4NTQyYWQ=

That being said, it works fine if you've got a headed server or in single player and has saved me hundreds of hours, so thank you for that :)

I have a similar issue, when running on an headless server, I can't convert blueprints to ghost on water variants, both the keybind and the button don't work

I can't replicate your issue, I tried running a dedicated server with you newest autosave and the same mods (but updated to to the latest version since I'm not manually getting the exact version you have) and Ghost on Water seems to work perfectly fine on a dedicated server for me.