Roofing, Gutters and Waterproofing - Drip edge fascia leak

I've been experiencing water leakage under the drip edge. The water runs down the fascia behind the gutters or, worse, in back of the fasica and onto the plywood soffits. The problem seems to have started when we had new shingles installed. The new shingles are 3 in 1's and the pitch of the roof is 3/12. Before the new shingles were installed we had T-lock shingles and didn't experience the problem. The drip edge seems to be installed properly with it running over and into the back of the gutters. I've been told that 3 in 1 shingles are not recommended for shallow pitched roofs like our 3/12. Is that true? Will installation of T-locks again eliminate the problem? Any help would be appreciated.

Some roofer will cut the first row of shingles longer so water can slide inside the gutters and not between gutter and facia...it works 50% of the time.This is especially true if you have an old gutters system you don't want to replace.

Sometimes the drip edge will not lay flat on the roof, and will be kicked up on the edge- sometimes due to the gutters spikes and ferrules. So a 3:12 pitch can become 2:12 or worse at the very edge of the roof. You might see if that's the case.

Other times, novice roofers will accidentally line up the seam of the starter row with the spaces between your 3 tab shingles. This will definately create a leak. You could also check that by lifting up a few tabs on that first row. The seam in the starter rows should be about 6" from the edge of a tab.

Did the roofer shingle over the old shingles or did he tear off? Assuming he tore off, then I hope the drip edge was replaced from the get go?