Why does a selection of LED lights only work in one color

I have a beautiful prelit LED Christmas tree that we love that we bought a few years back at COSTCO. With a push of a button, it changes to coloured lighting or to clear. Unfortunately, there are sections now that only work well when switched to clear lighting. And then others that still flicker a bit even then.

I've fixed incandescent light strings before... they're a cinch... but this has me baffled! Has anyone here had any success fixing the lights on a tree like this??

Note that this tree only has one plug. Each section passes power through the place where the trunk connects.

I have a LED Christmas light tester... but it's not much help. And frankly... I don't understand why only one color would work.

Thanks!