Some 16-inch MacBook Pro owners appear to have identified a shared issue suggesting the MagSafe 3 connector sometimes fails to deliver the expected charge when their Mac is turned off and the lid is closed.
As outlined on Reddit, some 16-inch MacBook Pro Models, when powered off, are failing to charge if the MagSafe connector is plugged in. Instead of turning green, the MagSafe light flashes amber and fails to deliver power to the Mac battery. Some customers have contacted Apple Support to find a solution, with varying degrees of success. One user, in particular, said that after a lengthy back and forth, Apple Support decided to send them a replacement laptop.
So it's not just me then! I have the EXACT same issue. Went to the genius bar and they tested with a cable and charger that they have and it still had the same problem. They said they would order a new 140 watt charger for me to see it would fix it but said most likely it's a firmware issue but didn't really provide any evidence for such a thing. I went home and the next day I get a call from Apple. Someone was calling me to follow up and they asked me a bunch of questions and provided instructions to run a special diagnostics program. After I did all that they said they want to take my MacBook and its charger back and that they would give me a completely brand new MacBook as soon as they get one. I'm still waiting for that but that's where I'm currently at.
A video shared on Reddit shows that when the MacBook Pro is closed, the light on the MagSafe charger repeatedly flashes amber and is accompanied by the typical macOS charging sound effect. A consistent orange light means the MacBook is being charged, while green shows it's fully charged.
If a MacBook Pro is connected to MagSafe while turned on and it is then turned off, MagSafe 3 continues to charge the Mac as expected. The issue only occurs for some users when attempting to plug in the MagSafe connector when the Mac is already turned off. The flashing amber MagSafe light is an indication that something is not functioning as normal, and an Apple Support page includes steps for users to take to return MagSafe to normal operation. However, the steps don't seem to work in the reported cases where the MacBook Pro is turned off with the lid closed.
Not all 16-inch MacBook Pro owners face the problem, and MacRumors has been unable to reproduce the bug. Regardless, there are enough users facing the problem that Apple may address it in the near future.