Currently stuck on . The second hotend does not display AT ALL (see below).
There’s a blank gap where the second hotend should be, so it seems at least that the firmware uploaded correctly (about screen pictured below):
I have double and triple checked the hotend heater cable connections, thermistor cable connection, and the hotend fan cables for the second hotend. Everything is connected as it should be according to the guide. The fans on both hotends are receiving power seeing as they do both spin up upon powering on the unit, so it doesn't seem that the problem is pertaining to the fan power leads. Additionally, I also checked for any physical irregularities in the wires, and they all seem fine.