Tbh, after playing for such a long time, targeting problems still kinda plagues me. I found out tabbing through monsters is quite unreliable, nowadays I mostly rely on simply clicking on the mobs that I wanted to target (Yep I am a PC user). Makes me kind of wonder how console players target their mobs though. Also one thing might be worth mentioning is, you can actually set a keybind to target the mob that is closest to you, which can be handy at times. I hope this might help you a bit.