[bisonbison]

The more I tell you I'm convinced that I'm a solid winning player the more you're going to think I'm in denial

You should really post in Probability and ask: how often should a player who wins at a rate of XBB/100 hands expect a -400BB swing, where X = -1, 0, 1, 2, and 3.

For what it's worth, I think the observation (danemania?) that you may be a fair-weather player may be on point. You may have an a-game that will win you good money, but you may be easily pushed off your a-game by bad results, and your off-game may be a d-game.

Everyone is telling you all they can when they say: this kind of streak in a game as beatable (if admittedly variable) as Party 2/4 is very rare, and gets rarer as you move from "I am a winning player at 0.1BB/100" to "I am a winning player at 2BB/100".