According to the tech at my local Apple Store, 3rd party Qi chargers not expressly designed for the iPhone 12 line of devices can intermittently stop charging the devices. This is apparently because even though the actual wireless charging spec remains the same as previous generations of iPhone, the magnetic ring inside the device, that makes the mag-safe chargers work the way they do, leaves for a smaller charge coil inside the device, which in turn requires more-precise alignment for charging. This is apparently especially prevalent on stand-style Qi chargers, where the upright-standing device may not align with the chargers coils correctly.
One suggestion they gave me was to try putting my device down on the charge stand sideways to see if it would get better alignment. But that’s a limited workaround because now your Lock Screen is sideways.
Short of that, they suggested replacing the Qi charger with one expressly tested with the particular device I have (iPhone 12 Pro), preferably a brand that is certified by Apple, such as Belkin or Mophie. These are, admittedly, going to cost more than some generic charger on, say, Amazon.
