Hp printer lost network connection

I have seen this issue multiple times on the support site, with no real resolution offered. I’ll try anyway. I have a detailed diagnostic for you. 

New XB8 modem installed. HP printer connected fine and worked. About a week later, it no longer connects. Diagnostic sheet printed by printer says it failed the No Filtering test. Research indicates this is a MAC address issue. Accessing the settings for the modem shows that MAC filtering is set to accept all.

The modem and printer have been reset multiple times. with no luck. Three interesting points. 

1) other devices have struggled to connect, but all resolved themselves with a little help.

2) I tried entering the MAC address in a white list for the modem. The address includes the hexadecimal number BC, which I believe is one assigned to HP. When entering it, the BC is autocorrected by the modem site to BE. I cannot get it to accept BC.

3) at one point the modem was restarted. I tried reconnecting the printer at the same time. There was a brief moment when the WiFi is back on, but the internet connection has not been established. At this point, the printer successfully connected to the network. Once internet access was regained, the printer disconnected.

So, what’s the answer?