Just installed Peacock TV on a couple of Roku Ultras. The app won't start. I get a splash screen and then it goes right back to the home menu. I've restarted the rokus, uninstalled and reinstalled the app, even tried adding a micro SD card in case storage was an issue but so far I've never seen the Peacock TV app running on my roku's.
Support from Peacock and Roku have been less than helpful so far and rather slow to respond.
It won't start on any of them? I would suspect some kind of network problem. Try restarting all of your network equipment (gateway/modem/router) and all of the Roku devices. Is there anything abnormal about your setup like you're using a VPN or something else most users wouldn't be using?
For troubleshooting, if you can connect one to an alternate network like a phone's hotspot give that a try to see if it makes a difference.