why in bullet 1+0, opponent time seem never decrease at death?

Hi. I was playing a game and opponent had 3.4sec left, I saw it lowered to 2.7sec then shot up to 3.4 sec.. then next move it also went down to 2.7sec again shot back to 3.4sec, happened a few more moves till I got time outed. Is that even possible or a cheat mode??

It could be the opponent's lag compensation. (Lichess compensates for lag by adding back time)