Maybe you're clicking (twice) to move a piece and what you're seeing is the animation of the pieces moving. You can make that faster, or slower, in the settings (Game Display:Piece Animation
lichess.org/account/preferences/game-display).
In any case, please do not assume that anything you observe but do not understand is a bug. Additonally, this does not belong in this forum, but in Lichess Feedback.
