Only Mac OS Users can connect on AC5300 but not Android

So in the cafe I go to daily, I convinced them to buy the ASUS RT-AC5300 as their old router was a POS.

anyway, these days they are complaining that customers with an Android phone cannot connect but ones with iOS such as iPhones or iPads have no problems connecting. Laptops connect fine.

They are using Smart Connect on Firmware 3.0.0.4.380.3341

Any suggestions to solve this please?