I have original posted about this in this thread, but it sadly got closed by the time I got around to replying.
To answer Egrath’s questions:
First to correct myself, I didn’t use Rufus but Endless’ normal installer and chose the USB stick option.
Unplugging the external monitor made no difference, neither did starting from the USB with or without the monitor plugged in.
When I clicked alt+f2 nothing happened.
This makes it sounds like the the system simply doesn’t fully load for some reason. More evidence to this is the fact that when I shut it down and boot again, it asks me for all the set up options again, instead of continuing where I left off like it should.
As I might have mentioned, before this started happening, I had a USB installation and was able to boot it up and continue using the system whenever I wanted.
I also tried two different USB sticks so I am quite baffled what might be causing this.