https://matchcenter.mlssoccer.com/matchcenter/2018-04-28-la-galaxy-vs-new-york-red-bulls/boxscore lists secondary assists in "Goals and Assists" on the left, but the statistics for each player only include primary assists.
What does primary assists mean? The last player to touch the ball before the goalscorer? That's the way it works in England. https://www.premierleague.com/news/511768
MLS has been known to award or take away secondary assists the morning after the match, after reviewing the video. I think the review for stats changes is routine. The question of whether the second-last pass contributed materially to the goal can be rather subjective.
Yes. At any time, the "Goals and Assists" on the left should match each player's assists column. I don't have a problem with secondary assists being taken away as long as the page is consistent with itself at any given time. The inconsistency isn't any better than if a player was credited with a goal, it was changed to an own goal a couple of minutes later during the game, and MLS had it as a player goal in one place and an own goal in another part of the same page after the game.