Looks like the warnings are gone after the last update :(
Yipee
Just saw this warning for my opponent while playing 0+3 game, he was not quick enough to make a second move, and hey presto, a warning :)
Warning, ConwyCastle. Letting time run out instead of resigning will result in a temporary ban.
Warning, Lichess, untargeted warnings can seriously annoy your users.
Got the warning for running out of time just now in a blitz game. Hope that it will be removed in a future update.