On the macbook, can you press and hold the left ALT key on the keyboard while you click on the wifi logo in the right top bar?
There you will get a lot of additional info about the wifi connection of your macbook.
Check the RSSI, Noiselevel, TX-Rate, PHY-mode and MCS index.
Also, if you can, use a wifi-scanner on your phone for example to check of nearby wifi networks interfere with yours.
Just an additional thought: You didn't connect your AP to a 100mbit port right?
This will likely give you a good start to a solution.