Your dB scale for the vertical axis is way to wide. You should really have it between about 100 dB and 45 dB. There's no way to see what's going on at that resolution. Also, if bass is what you're focusing on you can adjust the horizontal axis to between 10 hz and 200 hz. Here's an example.
View attachment 49870
You can see a lot more detail with the higher resolution in this chart.
Ok so I went back today and did some more testing. Something funky is def going on with my Audyssey calibration. I decided to take a couple steps back and measure the subs alone with no Audyseey. Even if I remove the smoothing there is no null. I would say this is a pretty smooth curve (if I remove any smoothing it looks nearly identical) for no EQ or room correction of any kind and the dip seems to be driven by the crossover at 80hz.
I then added the mains back to the mix still with no Audyssey. The brown line is the new curve compared to prior graph. Def some funky stuff going around 80-90hz at the crossover point without any room correction.
Lastly I added back the current Audyssey correction. The teal line is now post Audyssey, brown is without so whatever it did is actually making pretty much everything worse, my takeaway at this point is I need to completely re-run Audyssey to see what the heck is going on.