The S9 and S9 Plus have band 71 and other 4x4 MIMO technology built into the modem that the Note 8 does not or at least not to the same extent. This could be one possibility. Apple devices, especially with Intel modems, might as well be dial up modems. The S9's have excellent radios in them! When i was out in Pierpoint, West Virginia for a few weeks over the summer, I was able to tether a laptop and play Star Trek Online with no lag for about a half hour a day with 1 to 2 bars of signal on band 2. That was one of the selling points to get my girlfriend to ditch AT&T.
What kind of speeds are you seeing on the devices themselves? I know you said the S9 is faster but how much faster are we talking here?
Chris asked a great question. Can you give us a speed rundown on your devices so we can see the difference?