It has always been empty for me. I bought Horizons at a very odd time (when it wasn't a DLC, but a separate product), and apparently I have a steam account, but I've always played outside steam.
Anyway, I found the problem. For some reason, lutris had added "/steam" to my launch settings for the client, and that results in this error. I'm guessing it can't find the steam libraries and therefore fails.
On the first part if you bought it in Steam then you need to download the game through Steam as their won't be any files in your account to download (as it expects you to get it through steam), they removed the previous hosted executable link from their main webpage and now new downloads are via a randomly generated link from the frontier account.
Second point the /steam command is a workaround that stops the UI from glitching out, however using it will obviously put the launcher in steam mode and that's where it expects to get updates from.
I have two accounts, with the non steam account I use lutris but point to my steam directory and let steam handle the updates. I do something similar on Windows too except with the renamed launcher trick.