Ubiquiti UCI only 40Mbps upload

Hi I have been enjoying the x2 2Gbps connection on my UCI, however, I am stuck at 40Mbps uploads even though I am supposed to get 300Mbps in the plan. I have seen many other similar requests for help. Can someone help me with this issue? My Unifi UCI is on firmware: 1.4.3 and modem version 2.1.1. Thanks!