And I came up with an idea for how to deal with this issue.
Every five minutes or so, the webserver should check if Steam is online. If Steam is not online, the website should display a banner or something on the front page that says: “Steam is offline! If you are missing units, please be patient; You will get your units back as soon as Steam is back online.” or something similar.
Or perhaps, instead of something on the website, maybe something in the game every time you join a server? A chat message, or a message you have to click OK on, etc.