For zapping the same post, I had the best success long pressing to zap multiple times. Otherwise I think I was canceling the pending zap since Damus gives you a few seconds to cancel the one tap zaps.
Discussion
Looks like that works!
I was scrolling, zapping individual posts, tapping and moving. I went back and looked at some of the posts and the zaps still showed the count down clock. I though maybe they would clear later, but based on my wallet, they didn’t. I decided o couldn’t one tap zap more than once so had quit trying multiple one tap zaps for the same post.