Thanks Larry!
Okay, I think I'm doing something wrong here .. Missing something.
I take those two certs and copy+paste them into my <name>.crt file, at the bottom of the file, which already has my main + 2 intermediates.
Start server.
Nope, still get error.
Swap order of the two new certs in the crt file.
Nope.
Remove the original two intermediate certs.
Nope.
Am at a bit of a loss to understand whether it's not working because I'm missing something very obvious, or because android chrome is just that finicky (and if this is the case, the steps I need to take in testing until solving the issue).
Any thoughts?
Stu