When I was in a queue, trying to join a server I got disconnected from Minecraft: I was able to see an error respond from the server (while I was re-joining to keep my position in the queue) like "Invalid login information" (I don't remember the exact message), so the only thing I could do was to click on the button "return to server list" instead of seeing my server list I was forced to re-do my login to Minecraft like it was the first time I was opening the Launcher (required e-mail & password information).
Consequences: lost my queue position