I've been using this plugin since the 2nd. I have it set to drop 1-3 crates. Despite that, it never drops more than 1. Is there a setting I need to double check? 

Are you expecting it to drop multiple at once? If so, then expectation is wrong, as it will drop at most one, then move onto the next monument.

When it drops a crate, are you seeing the ch47 immediately leave the map, or does it continue patrolling monuments? If it continues patrolling, then most likely the monuments it is visiting do not have drop zones. After 30 minutes of being on the map, it will leave, so perhaps it typically only has time to go to non-drop monuments before it has to leave.

That makes sense. I see it go around, but no matter how many monuments it visits, it only ever drops one crate. 

Please pay attention to which monuments it's visiting after dropping the first crate, and check if those monuments are in the list of monuments on the documentation page. Additionally, check the server logs when the plugin loads, which will say which monuments on the map have drop zones, in case my documentation is out of date, or in case you are using a custom map which has custom drop zones.

5 locations it lists in the log. It still only drops one crate per visit to the island.