Thanks to people constantly bragging about this benefit AC has sorted it out.

Latitude fares from Europe now book into K L S booking classes. AC has pretty well zeroed out all R space on long haul so you won't get an instant upgrade any more.

Conversely if you're in B or Y booking classes (if you buy latitude ex Canada) you can almost always still get an instant upgrade whether R is available or not.

That's what happens when you taunt AC with a unintended benefit - you loose it.