PhilVeale

After reloading the game, on the same save, the issue has gone away. No idea what caused it. NPCs have appeared where before there was nothing, so yeah, whatever this glitch is, affects all characters; player's party and NPCs.
 
Really odd, but manageable if it doesn't happen too often and a reload will fix it. I'll update this post if I find more occurrences or any seemingly reliable triggers.