First off to say I have multiple devices connected to the same Deco M5 working fine on both 2.4 and 5Ghz frequencies. 

Have done little research and found the Roku Express only uses 2.4Ghz. Found an article that suggests that the device does not work with channel 13 so used a sniffer to find that my 2.4Ghz network is using channel 6 currently so this should not be a problem. 

When I try and connect it sometimes works for a short time and then stops. This is a recent issue perhaps starting after a recent firmware upgrade on the Roku. The Roku Model is a 3930EU - Roku Express. Software version 12.0.0 Build 4184-AE. 

Signal in the room is excellent so not the issue. 

When connecting the Roku to the Deco network it takes a time and then reports a 0.14.30 error message. This relates to either  weak signal or generic cannot connect to to the internet. 

The recommendation is to reset the Roku. Have done this and also factory reset. No option to revert the firmware that I can see. 

Also tried setting up a Deco 2.4Ghz IOT network, again using channel 6 currently. I can see the network from the Roku and try and connect but it again fails. 

If I connect the Roku to my phone hotspot it works fine. 

Have also tried isolating the Roku to a specific hotspot without success.

Any other ideas other than buying a Firestick or Chromecast?

Thanks

Martin