Why does AirDrop only work sometimes?

I have two Macs in the same room. Sometimes, AirDrop works, sometimes it doesn't. It's so random I don't even wanna try it anymore, resorting to a flash drive, instead.

On the source Mac, I right-click the file, select share, AirDrop, then wait for the destination Mac to appear in the list (which sometimes doesn't even show my iPhone, sometimes it does). Then on the destination Mac, I open Finder, click on AirDrop and make sure "Everyone" is still selected.

Most of the times, the destination Mac won't even appear in the source Mac. And when it does, clicking it does nothing, more often than not. It's really a miracle the few times it does work. Absolutely no settings have been changed between the times when it did work and the times when it doesn't work. Any ideas about what I could do to improve AirDrop reliability? Thanks.