Any question answered...

It could just as easily be the cable. If the cable housing/liner ends haven't been finished properly, or if there's a kink in either a section of inner cable inside housing or a section of the cable housing, it could exhibit the symptoms you describe. If the bike was posted to you, a cable could easily have got kinked in transit due to poor packing.

I'll take a look in the morning and see what I make of it, hopefully an easy-fix! Thanks for the help.