Still happening for me as well. People will be on the server and it shows through the MP list not online. 3rd party sites see the server as up as well. Try to join manually and it shows offline as well.
If you refresh it enough it will show up or if you let the entire list populate it will sometimes let you join manually.
Contacted my ISP and they have no blocks on any of the server providers, or IPs, and everything is good on my end with no drops or issues. (They told me to contact my ISP to see if that resolves the issue)
Put a ticket in and got a stock response that did nothing to help out, so I gave up. Acted like no no one else had this issue even though I have experienced it with several servers and visitors to our Warbirds server report it several times a day. Its not the end of the world just irritating
Sorry to hear we arent alone with the frustration. Happened to me 3 times already today