SSH -L connection successful, but localhost port forwarding not working "channel 3: open failed: connect failed: Connection refused"

My lab runs RStudio on a server. A couple weeks ago, from my cousin's house, I successfully ssh'd into the server and pulled up the server-side RStudio through my local Firefox browser. Now when I try to tát access the server RStudio from trang chính (via my own router), it doesn't work...