It's all very confusing, really, 2 days ago I bought & set up a new Apple AirPort Extreme wi-fi router. Initially, nothing would connect to the 2.4 GHz channel, this is important because my collection of older Macs, in addition to the Kindle Paperwhite & Lenovo Android 7-in tablet all lack access to the 5 GHz channel.
Something changed or settled down in the last 18 hours, they all access the 2.4 GHz band just fine.