Hello
I appreciate your feedback!
The check for Limitedprofiles is indirectly there and on by default. You just have to use MinSteamLevel 1, as Limited Accounts are always level 0, and others should be 1 when they buy a game.
However I agree that the documentation is unclear in this regard, and will update it (including the need to purge the config).
If you have any more questions, don't hesitate to ask. Also if there are still problems regarding that topic, send me an steam-profile of that account who souldn't be able to join, so I can run tests against it.
Greetings
Edit: It could be, that its possible to check limited-accounts on private profiles, too. However to verify and implement that, I need a steamid of an limited account with their profile set to private.
If you mean by valid profile, users who didnt set up their steamcommunity profile, then I would need a steamid for that, too. I found some profiles in this regard. But they also were all steam level 0.