Somehow, even with solid infill area threshold high enough, solid infill layers have gaps under vertical extrusions (near the edges):
STL and config:
The gaps are not generated on this model when "extra perimeters" are disabled.
The problem became much more aggravated with a recent commit:
Don't trigger extra perimeters when less than 30% of the upper loops …
…would benefit from it. #2664. Also fixes #2610
Fixed as well.