For the past couple months I've been charging my pixel 3 using a wireless charging pad as the port on the phone itself is damaged but recently, starting yesterday, the phone refuses to charge past 0%, it will be completely dead (wont even show the red battery icon when its flat) and will sit on the pad for a good min or two then it will show 0% on the screen, after a few mins it will just randomly disconnect from the pad, ceasing to charge over 0% and will not reconnect or start charging again at all until it is completely dead again... I havent done anything at all different then what I have been doing for the past couple months, havent damaged it any more then it already was and its been sitting at home, keeping the charge above 40-60%. one thing I have noted is that the phone will get extremely hot while its charging
I had this problem on my Pixel 4. It was a "known issue" (manufacturing quality) at Google. They sent me a refurbed phone even though it was past warranty. And at one time I had googled my way into a technical description on one of the better known forums and I found description of something going on near the site of the charging port, a defect on the circuit board. It was a year ago and I'm sorry I can't be more precise. And it was not something with a DIY fix. I don't know whether it also applies to Pixel 3. I wasted a lot of time and money on new chargers and new charging wires.
So you might consider contacting google tech support. They will likely refer you to one of their repair stores unless they fess up to the manufacturing error. The whole return replace process for me took a couple of weeks. I purchased a $150 Samsung to bridge the gap (you know, like having a laptop in case the desktop fails). I can tell you something. For sure when using that inexpensive temporary Samsung I knew I was using an idiot child compared to the Pixel 4. Everything about it was slower: turning it on, opening apps, surfing the net. And in texting the dictation feature was worthless.
Unrelated to this particular case, but good to know, is these magnetic charger thingies. They are breakaway which keeps you from stressing the charging port by jerking it accidentally. They also plug the open port freeing it from dust and grime. The magnetic buttons do tend to stop working after a year or so, I think because the glue/solder inside fails. But they're cheap and easy to replace.