When my Gen 4 G19 was new, I would get BTF (Brass to Face) about 1 in 20 shots. In the last 1000 shots I've fired, however, I can't remember even one BTF. Before that it was maybe 1 in 50 or 1 in 100 after about 500 rounds.
Give it some time, call Glock, or just take it to a gunsmith. Any of these are likely to fix the problem.