Latest firmware(s) (partially) restricted UART access?

[fonix232]

My G4 is on the latest firmware - unfortunately I've only recently found this repo so it didn't even occur to me to keep it on the lowest possible version.

I've soldered the appropriate test points, verified cable integrity and continuity (none of the three are shorted to the others, both Rx and Tx test points and cable ends show a ~3.3V difference to Gnd), and hooked it up to my know to be good serial adapter, with PuTTY as per the documentation.

While pressing Enter does seem to interrupt the boot process - based on the LED, which stays yellow - however I'm getting absolutely no output from any command I enter. I can see that the commands are being executed - for example if I enter run bootcmd, even though there's no output through the terminal, the chime continues the boot process, obvious from the LED changing to blue, beginning to blink (looking for WiFi or possibly the doorbell itself), then settles on static blue LED.

I've tried re-soldering the pad thinking I've messed it up, but no, even with the cleanest solder joints and as per above verified cable status. Unfortunately executing the guide's commands results in no change, and since there's no visible output, I can't confirm if the given commands even run properly or not. What I know for sure is that I get no telnet client on startup.

HW Rev.: 1.1 Firmware version: 4.0.6