5ghz connect issue with android Galaxy S8?

Have sudden issue connecting with my Verizion Galaxy S8 phone. Thought it might be something going on with the router/LEDE, though it now seems to just be this phone, on 5Ghz only. Wife's IPhone works on.both bands, as other Wi-Fi connected items. I had a SW update on the phone several days ago, probably the source.

Anyone hear abt this? I will ask in some S8 forum when I find one, but thought mentioning it here might find me a clue. Symptom is, phone connects to 5Ghz, then gives a msg saying "checking quality of internet connection" and disconnects in a matter of seconds. That msg seems to be new, might be part of SW update. The 2.4Ghz goes thru all of the above, and stays connected and runs fine. Only just noticed I'm always linked on 2.4, since both are available and on autoconnect.

Rebooted the router, and as I expected, no difference. Of note, was 10hrs from a round 60 days of uptime, since loading the current 17.01.4 on my C7. Bummer, blew my run for nothing... Had something like 129 days on 17.01.2 on what's the sole house router, would have been longer if a power fail didn't reboot it earlier.