If you landfall loyalty gems it doesn’t trigger landfall abilities. It should.
This is taken from the first preview of landfall mechanic: "Landfall is a keyword that is present on some cards. It is triggered by matching 4 or more colored gems. "
So it states colored gem, loyalty is not included.
Also it makes more sense this way as a transposition from paper magic cause the 5 colors represent the 5 lands.
That is where landfall mechanic come from.