Can’t reconnect smart plugs to sky hub

[Baileysmum]

My smart plugs have been connected for years with no problems. All of a sudden they stopped working with Alexa but I could still control them via the app on my phone. Their status keeps showing intermittently as offline in the app.

I uninstalled one and now it won't reinstall. I've updated  the app and Alexa, rebooted the hub, split the channels to connect to 2.4 (even though I've never had to do this before) but it still won't connect to the app or network. I accidentally uninstalled another plug and now have the same issue with that one as well. 

Any ideas?  Thanks. 

[Baileysmum]

I've also tried to connect in EZ mode but it fails.