Setup
Main Deco unit is connected to ISP modem, this main unt also has a four port switch connected. There are two further M4 units one connected by cable via the switch connected to the main unit and the other via wireless backhaul.

The switch also has the Sky TV box, alarm system and TV connected.

The issue
The units lock up, all units have a solid ref light.  Power cycling the main unit brings the main unit and wireless connected M4 back online, with the cable connected M4 needing a seperate power cycle.

These lock ups only occur while streaming Prime Video and Disney apps via the Sky TV box.  

The connection while not using these apps through the Sky Box is solid.  Watching any streaming services via tablets or mobile devices connected to the network is again solid.

Having read some previous threads I have tried disconnecting the Ethernet cable from the main M4 back to the ISP modem but that doesn't rectify the issue.

There is also mention of putting debug software onto the units, however I don't know how to do that.