Resolved
With the legacy UI it is possible to edit Content Templates with page builders such as Avada’s Fusion Builder or Divi builder.
This broke with the release of Toolset Blocks 1.5/Views 3.5.
When pressing the Edit with Fusion button the page simply reloads, without launching the pae builder.
This is fixed in Blocks 1.5.1/Views 3.5.1