Wordfence: Can't disable Falcon Engine

When I try to change the caching settings in Wordfence from “Enable Wordfence Falcon Engine” to either “Enable Basic Caching” or “Disable all performance enhancements,” I get a message saying that the change has been made, but the setting doesn’t actually change.

For various reasons I’d like to observe the live traffic to my site for a while, and then re-enable Falcon, but I’m stuck!

Any ideas?