@Grant_ disregard, followed the directions here and it resolved the issue: https://community.tp-link.com/en/home/forum/topic/197502

RE505X will not connect to 5ghz Wi-Fi band of AT&T Motorola BGW210 router. Both 2.4 and 5.0ghz bands have different SSIDs and I can connect to both on all devices except for the extender. Tried both...