Key chatter / double-pressing problem on multiple Flatbox builds

[Soundtoxin]

Have you run into erroneous double-presses on any Flatbox rev 5s you've built? What are some possible causes? To test, you can bind letters and such to keyboard mode keys in GP2040-CE and type in a text editor, or in xinput mode you can use something like Steam's virtual keyboard in the chat and see if you're getting multiple letters per press or if your dpad buttons move multiple places on the virtual keyboard.
I've run into this issue on at least two Flatboxes, I suspect all 10 I built have this issue but they're no longer all in my hands to test.
I do not have the issue on a Haute42 G16 from Aliexpress running the same firmware, or on an Open-Frame1 I built running HayBox firmware. The G16 and Frame1 have MX-style switches in common while the Flatbox uses chocs. Everything mentioned uses hotswap sockets.
The latest RC GP2040-CE firmware added a debounce setting in the web configurator that I played with a bit. Default is 5ms. If I crank it all the way up to 120ms it solves most of the chatter (I tried many lesser amounts along the way with less luck), but that's a ton of latency and shouldn't be necessary. I'm trying to track down what went wrong but there are so many variable.
One Flatbox I tested is using choc silvers and another is using choc whites.

[Soundtoxin]

Someone I spoke with said that maybe the MCU (RP2040-Zero) is lacking the proper suppression to deal with USB noise.