Same issue, iPhone 12 not charging, LED on wireless charging stand starts blinking.
Here is the charging hardware specs:
Monoprice Fast Wireless Charging Stand with 2 Coils, 10W, Qi Compatible
Monoprice Obsidian Series USB Smart Charger with Qualcomm Quick Charge 3.0 technology.
I have 2 sets of these as well as 2 iPhone 12's (iOs 14.2.1 on one phone, 14.4 on the other).
I interchanged/swapped all of the above components, including the USB to Micro USB cable. I even switched AC power sources where the charging adaptor was plugged in to. I pulled phone covers off. It starts blinking before 5 minutes are up. I also switched phones.
The most bizarre thing (I have both chargers on our king size bed headboard) is that the failure at this moment stays on the same side of the headboard, even though I've entirely swapped all components from one side to the other. However, let it be known that the same thing happened on the other side of the headboard over night while I slept.
The charger on my side (the side that is working correctly at the moment) was blinking when I woke up today, and I had only about a third of charged capacity on the battery. It should have been fully charge. I have had these brand new phones for a total of 4 days. Each phone has a different case (Otterbox Prefix Series, Casekoo Defender), but that's on non-issue since the problem is present with the cases off.
Frustrated, I put the phone on the problem side directly on a cable connected to the phone's charging port; it's charging correctly.