Printer visible in AirPrint list, but printing does nothing

[MikePaer]

My Brother DCP-7065DN printer gets configured fine in CUPS and printing test pages works. It also shows up as an AirPrint target on my iOS devices as expected. But when I click print on iOS after selecting it as the AirPrint target, nothing happens. Nothing prints, ever, from any iOS device. I don't see anything obvious in the logs. Any ideas?

Note: when I set up a fresh Ubuntu VM and set up CUPS/Avahi manually, AirPrint from iOS works. But when I shut down that VM and instead spin up this docker container with the same CUPS config, AirPrint from iOS does nothing.