Look, obviously if you're making gains there's no reason to complain, but if you get to the point where you're doing 15 reps on your three rep day, you need to increase the weight.
The problem with programs like 5/3/1 that only increase the weight every month is that is doesn't accommodate for newbie gains (which isn't a criticism of the program, since it's not meant for newbies.)
I've been on 5/3/1 for about 7 months now, and I've run into that problem quite a few times. Sometimes you find something in your technique that really just clicks and you blow your PR out of the water. For example, I did 335x13 on my 3 rep week in the deadlift and 240x8 on my 1 rep week on the bench. At that point, I'm not training in the rep ranges that I want. It's okay to increase the weight, but don't increase it to the degree that you're only getting 5 on your 5 week, 3 on your 3 week, etc.
TL;DR: Modify the weight with caution. In my experience, don't artificially inflate your training max to a weight that does not allow to to perform at 8-10 reps on your 5 week, 6-8 reps on your 3 week, or 3-5 reps on your 1 week (preferring the high said of all of those rep ranges.)
Just my $0.02