Unbearable coop lag (STILL)

Anyway, I just tried to do H4 coop and the lag was unbearable to the point that shields would be full and then be red while teleporting all over Forward Unto Dawn.

why is there no fix for this still?

There are different types of lag, which can not be fixed, only reduced. I believe what you are encountering is latency or Internet lag. Internet lag is usually a result of being geographically far from the server host. This is not something you can fix with a magic button, but getting FTTH will help. There is also FPS lag with is client side, maybe your friend had family members all on the same network, with devices such as Cable TV, smartphones, tablets, and other computers all accessing the Internet at the same time. Lag sucks, I know. I can barley play with my friend in Idaho w/o encountering a jitter. Then again he is us ally doing other things as well.