Hi Chipp - it's going to be something on the reverse side - filleting tends to not like to have pieces that are part of the same plane, like these here:



So I went to delete those 2 faces to build one single big plane there to see if that would help, and after deleting those pieces there is left a stray edge right between them:



That's actually a really skinny little surface fragment there, that's likely to be what is causing the fillet problem, it's a kind of little teeny shelf or needle sticking upwards from this side here:






That thing is likely to be the source of the fillet trouble in that particular area.

- Michael