That sounded like the solution I was looking for, tried it, didn't work. Tried each track that won't select, but nothing ticked/checked in “Arranger Exclude“ to begin with. Tried enabling, and then re-disabling, still nothing.
EDIT:
Ok, just found the solution. Any track that had Melodyne as a region effect would refuse to select. Bounced track to clip, and it will now select. Strange. Also inconvenient as now lose the ability to turn off RFX on clip.