So you mean, the server stays online as long as it has 1 player, but goes offline randomly when someone else joins?
Also, your server is running plugin(s) such as VanishNoPacket and EssentialsX which are used to vanish. And as soon as you're go in vanish, Minehut thinks that your server has 0 players online, and looks forward to despin it after 5 minutes.
One more thing, can you show your log file contents after the server goes offline fully?