I bought a bunch of 3.3V pro micros that appear to have real atmega32u4 chips on them. They identify as real briefly. I'm using Xubuntu 16.04 (uname -r 3.13.3-170) with arduino 1.8.7 on one machine, and xubuntu 20.04 with arduino 1.8.13 on another machine.
On both machines, I can plug the chip in and see it show up in dmesg and find it in the arduino IDE, check the board info, I can upload blink, and once I do so all the LED's come on, stay on, and from then on the board refuses to enumerate as a usb device.
Example of dmesg once I've tried programming it once:
[467519.580143] usb 3-1: new full-speed USB device number 14 using uhci_hcd
[467519.700150] usb 3-1: device descriptor read/64, error -71
[467519.924195] usb 3-1: device descriptor read/64, error -71
[467520.140156] usb 3-1: new full-speed USB device number 15 using uhci_hcd
[467520.260134] usb 3-1: device descriptor read/64, error -71
[467520.484124] usb 3-1: device descriptor read/64, error -71
[467520.700160] usb 3-1: new full-speed USB device number 16 using uhci_hcd
[467521.116074] usb 3-1: device not accepting address 16, error -71
[467521.228112] usb 3-1: new full-speed USB device number 17 using uhci_hcd
[467521.640149] usb 3-1: device not accepting address 17, error -71
[467521.640247] hub 3-0:1.0: unable to enumerate USB device on port 1
This has happened with four devices, on two different machines.
I have tried hard-resetting them once, twice, 20-ish times, with no success.
There's no delay in booting whatever it's doing at all: I plug the board in and immediately the LED's turn on, and dmesg blows up (although it does show repeated additional entries as the usb subsystem repeatedly tries to get the chip to enumerate.)
I hooked up an atmel avrisp to one, reburnt the bootloader, it claims I did it successfully, but the chip still refuses to enumerate after burning a new bootloader.
I also have a 5V pro micro. It works fine every time.
So, if you're using linux maybe don't get 3.3v pro micros.
I'm open to suggestions. I have one left that I haven't yet destroyed by attempting to program it.