Thanks for this.
Our tech team have found the issue - the keyboard on some Android phones is hiding the button. I don't mean that in an obvious way that we humans imagine a button being hidden, but in a complex geeky way (which I confess I don't follow 100% myself) means the button is made really, really small.
Not all Android handsets are doing this. We're getting thousands of readings every day from Members with Android phones.
It'll be fixed in an app update soon