After pull request #16989 a draw offer is turned into a claim that immediately ends the game if the opponent does not have any mating material. This makes sense, but since there is currently no indication why the game suddenly ended in a draw, the opponent will be left puzzled what happened. See the following forum posts:

https://lichess.org/forum/lichess-feedback/draw-indicator-for-insufficient-material
https://lichess.org/forum/lichess-feedback/game-ended-in-a-draw-for-no-reason-2