After more than a year of frustration, I stumbled on this one, simple fix; "enable jumbo frame." Could it be that easy?
Everything was great with my old nighthawk router. Going to an Asus GT-AC5300, ($400) things started going wrong. I used a static IP as my last ditch effort before pricing this MF4880dw in the trash. Got it to work but spotty. I'd have to reboot the printer and it worked until it went to sleep again.
After ready this post, I thought I'd give it a try. Why not, right? Bingo, that was it... The print admin page showed up with the printer in sleep mode. This "fix" post existed for over 5 years and in so happy that I stumbled across it. Thanks rsg343, I owe you one.