@David-TP 

thanks for your reply.

this Deco unit is one of 5 I have in my mesh system and it has been working fine for the past few months.

to answer your question, in the Deco iphone app I can still see the unit but it says that it is 'offline'.

please let me know if you require more info.

  @David-TP 

given that the unit has already been set up (not being set up now) do you still reckon I should remove it and add it again?

  @C-Mans If the unit is flashing blue, the unit is not aware is is part of a mesh, and the unit is awaiting to be setup.

As you did a hard reset, the app is not aware the unit had been removed from the mesh.

When you use the app to remove a unit from the mesh, the app is aware, and the app instructs the unit to reset itself.

I suggest removing the unit from the app (if possible), and adding it again.

If the unit was the main unit, removing it will remove the mesh from the app, which is fine.