Manu, well done on finishing!
I haven’t attempted the puzzle, but can see how it works.
The wordplay in 17 seems to yield “fullmeg” (where fug is “close atmosphere”, ll is plates and setter is me) which gives the “Meg” for part of “megrim” (vertigo in 19).
But “meg” is indicated by 20, “megimp” (mig reversed in mep).
So we seem to be missing the “rim” part of megrim. This was the conflict that the poster of the old thread I found was referring to I recall.