Rare spawn enemies weirdness ... or not?

So, I don’t know if this is weird or not… I just finished a playthrough with Moze (solo, always), and almost every rare spawn popped. Like every time I was in the area. Without even trying for them. Then I went back to my Zane to bump him up to 53, and zilch. Just like the first time I played him. Never, nada, no rare spawns to be found.

I understand it’s random, and chances are better if you’re not playing solo, but still - it seems odd that the randomness is so… unrandom. Always for one character, never for another. Am I missing something?