I'd check things out although the heavier fmj may cause an arrow to drop like that from 20-30. Dropping like that from a 100 head to a 125 shouldn't happen on it's own I'd say.
I've been shooting bows more than 50 years and I've
never seen a 25 grain change in tip weight cause a 3" drop at 30 yards. If the bow is set up right and the shooter doesn't change his form (ie. dropping his bow arm to peek andsee if the heavier tip is changing his arrow flight) 100 gn tips and 125's will shoot to the same exact spot at 30 yards- as long as the extra weight doesn't cause spine problems.