I've configured a dual setup router, and the main one is wrt1900acs with the last build (davidc502) but pretty often the 2.4 and 5ghz disconnect. And not always able to reconnect. The 5ghz band is worse. But on my second router (vpn) netgear R7800, everything is fine.
The mwlwifi wifi driver in the WRTxxxxACx series has not been maintained for a year, as the manufacturer abandoned it. Depending on the client hardware and driver, there may be intermittent problems.