QR code scanning troubles

Ah, that gives me the important clue. This is a macbook pro (15"2018) with an additional external monitor. It fails to find the QR on the external monitor, and the easy workaround is to drag the window onto the laptop screen.

So, that's where your engineers can look for bugs. Mix of multiple displays, resolutions, and DPIs. Laptop screen is default retina resolution, arranged to the left. Monitor is arranged to the right and at a different resolution (its default, happens to be widescreen, 2560x1080). Dock/menubar moved to external monitor.