Hi Barnaby-
Thank you very much for the detailed replication information. I was able to replicate the bug on a physical iPhone, but strangely not on our normal cross-platform testing service, browserstack.com.
It looks like the Javascript that computes the z-indexes of the images is not executing the same way on Apple devices as it does on other hardware.
I’ve gone ahead and filed a bug report for our developers.
Right now, due to our work-from-home pandemic policy, I don’t have access to our Apple devices at our office to try and give you a workaround solution. I’ll update you here as soon as we’ve got a possible fix for you.