No, there was nothing plugged in, just power through USB-C.
I tried installing the firmware through another wifi and it worked. Now the diagnostics pass clean.
I don't know what could have caused that.
I've just bought the Pineapple Mark VII and after running the diagnostics (/diagnostics page) I get the Storage Test 1 -> Failed.
Any clue on what could be causing that and/or how to fix it?