An interesting thread! I'm speaking as one who had cavity wall
insulation installed about a dozen years ago.
I didn't like the look of the guys who did it, although they were
surprisingly efficient, or should I say "fast" -- did the whole house
(60s 3-bed semi) in a morning iirc).
Having read the thread so far, I expect to see the same guys (or rather
their mates) again fairly soon, to "check the installation".
I have one damp patch, at the foot of the wall adjoining the house next
door. Might not be to do with the CWI, but I've always had my
suspicions. That wall faces directly north, and never ever gets sun.