Update:
I finally managed to find some of my zen and sanity to calmly look into my cabling issue. I ended up replacing the expensive outdoor-rated cable with a cheap one from Amazon and voila! it worked! I have no idea what caused the old cable to show ok with my cheap cable tested but causing issues when connected. It's the first time I ran into this issue, I had crimped various cables at my old house.
@netstruggler thank you for all your input. May I ask you what tester you use to test speeds? All I have previously done was connecting the ol' laptop and go to testmy.net