hi @GrahamCox sorry but I can’t help you with this as I can’t replicate this as I do not own any Android device and behaviour as you describing should be an issue on Android OS. I have tested increasing font size on iOS and I was able to increase size to 200% without any structural change.
When font size increased over 200% the burger get pushed under logo so it have normal behaviour as it is flex and doesn’t fit into screen. It should behave identical in Android, but I have no Idea why isn’t.
If you do not have further questions related to original topic and problem doesn’t persist, feel free to close your request as solved