So a bit of a breakthrough for me. I experienced all the same problems described above. Infuriating.
Then, I realized that due to the way my phone was rendering the QR code, a portion of the QR code was being hidden by the text box that says “I heard QR code scanned”.
I used my finger to slide the image up slightly, revealing the full QR code (the bottom 5% was previous obscured) and the image scanned within 2 seconds.
I am pretty convinced this is the root of these problems.