Purple arrow?

Put a position into Analysis board and moved a piece and a popup with text "Purple arrow...........", as well as a purple arrow, appeared and disappeared in an instant. Tried to search what this is with no avail. Apologies for my ignorance.

May you tell me what you problem is?

see lichess.org/forum/lichess-feedback/arrows-appearing-but-not-wanted-or-requested

Purple arrow indicates the move that was played in the game (the mainline), to differentiate it from other arrows, like variations (pink), best move arrow or infinite analysis.

Yeah that happened during when I was looking at a study