Don't Starve Together server status checker
Don't Starve Together runs as a cluster of separate shards, each with its own port, and only the master shard answers queries.
Which ports a Don't Starve Together server needs
A standard cluster is an overworld shard and a caves shard, running as two processes on two different UDP ports. The master shard's port is the one to test — querying the caves port will time out even on a perfectly healthy cluster, which is the usual cause of a confusing result here.
If it still shows offline
Check the master shard's port specifically. If it answers and players still cannot join, confirm both shards started: a cluster whose caves shard failed to launch will accept connections and then break when anyone tries to descend.