There's sub, and there's sub-sub.
I'm no expert, but I've been spending some time looking the output of some bass music "pros". 50 may be way too high to cut for a lot of music, but there's still work to be done below 40 or so.
Here's the kick on a track by "Bop" (awesome minimal D&B)
Here's a raw kick (from an EKS Pro):
(a little bit of apples and oranges - hard to capture the images and different kicks).
Point is a lot of raw kick/bass sounds still have some unused energy down at 20-30, and my guess is it affects the limiter by introducing distortion - you may not hear something at -36 - -48 db, but it's there.
Here's the same kick with just a bit of low cut:
I don't have subs here and so can't hear the difference, but most of the tracks of looked at have a similar spectral signature.
I suggest trying something similar - I never use EQ like that without an analyzer to see if I'm touching any of the energy of the sub sounds (and there are times a very sub-by bass note will need a little more room), but betting it helps.
I'm also using Ozone - you really need a quality limiter to get good results across the full spectrum without distortio.