I did see that one but guessed you would be using the smaller, Wavlink one, also with the AC600 name.
You seem to have chosen the most appropriate model, and I've not seen anything so supportive of Linux, unless there is something very different about Mint 19 c.f. Mint 18.
I can't think of anything else except checking the WiFi settings very carefully - which I'm sure you will have done several times.
Keith