Stockfish resigned on horde mode

I was trying to check if lichess would detect insufficient material to win on horde mode. After a few moves with only my queen vs his king, Stockfish resigned. Never saw the computer resign before. Is this a bug?

computer always resign at move 151

Indeed, AI level 2 (or any AI level) used to refuse to play after move 150; now it simply resigns.

There is no "insufficient material" since Black can always win. I forget whether a 50-move rule draw can be claimed by either player (in general, not in this game).