Slow Upload on R7800

I've been having an issue where my Netgear R7800 has very low upload speeds (~0.30 Mbps) compared to when I'm plugged directly to the Spectrum modem (~25-30 Mbps). Download speeds on the other hand are fine. It's clear the router is the middleman with the problem, however I can't seem to solve it.

I tried numerous fixes I could find here but none of them work (e.g. I factory-reset the router, I downgraded to an earlier firmware, I switched cables, I turned off QoS, etc.). 

I don't understand where this issue could be coming from at this point.

Any help would be appreciated!