https://clips.twitch.tv/ObedientConfidentRamenM4xH...
When you gonna make a purple trigger, such a purple-yellow is called "Devil Pair (デビルハチイチ)" in Puyopuyo term.
The probability picking this pair is 2/25 (in fact 2/9 is suitble) so that I think it's OK if you chalk it up to bad luck.
You can avoid the devil pair by an extra splitting but It's also an act that slows down the extra time.
To address the other points, I recommend to put it on 5-6 columns.
This chain seems to be mainly a 4-double from middle greens, so I wanna use green in route of the chain from green trigger, although with a splitting.
About caring a devil pair, I often take care of a chromatic devil pair (2/9), but I rarely do of a monochrome devil pair (1/25).