I have noticed this as well. It is very inconsistent about "lighting up" the zap icon. However, I can usually see my zap in the list of people who have zapped the note.

Unlike some clients, Amethyst only seems to update the icon to show that you have zapped the note once the zap receipt is received. During that wait, there must be some kind of time-out that won't update the zap icon if the receipt isn't received promptly.

Or it could be an entirely different issue that I am completely unaware of, since I couldn't code my way out of a paper bag. 😂

This is one of the things I like about how Primal does it. The zap icon is updated right away to show you zapped, and that is only removed if no zap receipt is received.

Still prefer Amethyst over Primal for a number of other reasons, though.