When using Kali Linux on a Raspberry Pi Zero, my standard headless setup is to use an adafruit console cable: https://www.adafruit.com/product/954 plugged into the UART pins on the Pi and then into my desktop or laptop to access the console. I had a fully working setup with an older version of kali on an 8GB card, but decided to upgrade to a 16GB one and the newest image, which I did last night. The issue is as follows: when booting, several garbage characters like line drawing characters and fully filled in squares come in at the top of the screen. Sometimes, the entire output is this. However, normally one the login screen is output everything is fine, and I can login. Once I've logged in, everything is fine for 1-2 minutes, and then all text being sent in gets messed up. Most characters echo back as "n", "~" or "▒". This means that obviously the serial console is unusable, and I'm forced to do a hard restart.

I'm reasonably confident it is an issue with Kali Linux, as after switching out the Pi zero for another board, switching out the laptop and moving from BeagleTerm to Putty, and switching out the SD card, the issue persisted. I also tried booting an OpenWRT image and multiple versions of Raspbian/Raspberry Pi OS, and all did not have the issue.