For anyone who is interested -
I went back down to the basement and did some more troubleshooting. I changed the wifi channel on the LCS unit (from 1 to 5; no idea why I chose 5). Now connects as before (green link icon) but now amber light on base is blinking and iCAB app seems to be working (for now). So perhaps WiFi interference was the problem (?) and just because the link icon is green must not mean the connection is necessarily robust.