There's a dedicated thread here for servers with "Unknown" status. https://www.survivalservers.com/forum/index.php?/topic/3148-have-a-server-status-unknown/ I know it may feel more effective to make a new thread, but the admin is likely monitoring the existing thread for sudden bumps. New threads will get lost in the general unread mayhem.
Is this from the ingame server browser, or the Steam one? The in-game one has known issues and will only display a certain number of servers.
Fix 1) In Steam, navigate to Views > Servers. Filter servers by game and find your server. Add to favorites for future reference. You can connect directly from there; it will launch the game.
Fix 2) Is your server the same version as your client? You may need to search with "invalid servers" option enabled. Be aware you will probably have to update your server before your client connects without crashing. (I know you said you checked this, just listing for others )
Server ID #34679 Also ran update/validate, tried saving config file. Still unknown. Everything I try to do, including restarts, is super slow compared to the previous 2 days.
Edited to add: Now stuck on "loading" instead of "unknown"