Actually it is just half a solution as Delay node just after the receive execute can lead to other issues, not bugs, but it interferes with tick events and such on the actor and eventual children or other dependent actors.
Also, 0.1 second is quite a long time but it does not seem to work if having a shorter delay (for real it depends on the scripts, some accept shorter delays, I guess it depends if the leading blueprint is heavy or not) .
I guess the only real solution is to go through C++ instead of blueprints but then it is quite sad for non-programmers 
… Anyway, thanks for your answer Sean Flint !