We had this on Caroline's Mercedes E350 Coupe when it was 5-6 years old.
Mercedes re-sprayed the car under warranty.
I was told that all Mercedes cars painted a particular red and between specific dates had the problem.
The cause was an unexpected reaction between the primer and the first colour coat, due to a formulation change in the primer. The paint maker didn't think the change was sufficient to need to be declared. The bubbles lifted the clear coat slightly.
You don't say what the colour was, but it does seem to have a greater frequency with red pigments. Very strange.
Tarka the 'Otter Mog
2014 Plus 8