As of this morning, both clients behind the 880L bridge running the latest 1.20 beta firmware have been cut off from the internet. The client on DHCP lost its IP address lease. The other client on static IP running syslog server also cannot access the internet. The 5G radio LED is slow blinking.
The syslog server captured only a few log messages. I have taken a screen image but don't know how to attach it to this message.
It seems like with 1.20 beta firmware, the 5GHz link between the 880L bridge and the Netgear R8000 router becomes broken after a while. With 1.08WWB04 firmware, the clients can remain connected to the internet for many days.