Our garage door has started reversing on the down cycle.

It does this sporadically. It can give us fits not going down, then the
next 25 times we need to lower it, it goes down great, then it'll give
us fits trying to get it down, and so on.

The electric eyes are aligned properly (an led glows steadily if they're
aligned, and blinks if they're not). I wiped away a good amount of dust
and pollen from the lenses and around them, so they're clean.

The door seems to go fine when I raise or lower it manually. If I go
fast or slow, I can move it all the way along the track with one hand
quite easily, never encountering any resistance or kinks.

So what else should I try?