Something changed in bullet chess?

Since some days I face following problem when playing bullet chess (1min without bonus):
I get into a won endgame with both players having only few seconds on the clock. However I have some seconds more than my opponent, so I begin to some play legal premoves (my king can't get into check). After this my display freezes for several seconds showing 3,5 seconds for me and 1,5 for my opponent. After this, suddenly chess.com displays my game as lost on time (happened with game id=489918341).
That's very frustrating since it happened now a lot of times to me last days on won games always in the same manner.
The weeks and months before I have never seen this problem on chess.com

Try clearing out your browsing data :) It sounds like it may be browser related lag.