here's an example:

i started up a scottish league season, playing as Celtic. everything was going swimmingly, until i noticed that in every single game i played, i was in the home green-and-white stripes, never the road black. this was especially annoying when i played Hibernian, as both teams came onto the field in their home green-and-whites.
what gives? i've flipped the "kit clashing" toggle both ways, doesn't help for the most part.

no matter what settings i use, what mode i'm in, or what teams i'm using, away uniforms are NEVER used. why? how do i fix it?

Try going to Edit Teams and changing the away jerseys.Thats the only thing I can think of.