I use my airpods all the time and especially with the double tap to siri.
Lately however this stopped working.
When I looked at the settings it was still enabled, but just did not work.
I could not find any reference to this in the airpods documentation on the apple website.
But looking again (with magnifying glass) I could see a VERY small footnote that mentioned that in order for this feature to work reliably the iPhone needed to have the setting “allow siri when locked” enabled.
As I had disabled that following some new lockscreen bypass issue it obviously no longer worked when the iphone was locked.
It is weird that such a significant setting is burried somewhere in a footnote…
I just thought I’d write this up so it might help someone else with the same issue save some apple website searches 