Using windows 7, with acrobat DC.
Ive got to say ive found the Fix Hairlines methods outlined here to be very POOR at best. Honestly, after many many test files i would consider it to be bugged.
Ive even had it delete lines entirely, when i clearly told it to increase line weights.
If someone from adobe would like to contact me i can provide test files and preflight profiles which DONT do what they say they should.