Recently I received an HUAWEI HG695 router. It has a dual band wireless for 2.4 and 5 Ghz. But even the 5G was enabled on the router it did not show up on my wifi-list on my iMac, iPad and MacBook.
The answer lies in one advanced WLAN setting:
Change the bandwidth from 20Mhz to 20/40Mhz and all works like a charm.