Hi @kjetilbmoe As indicated in "Still not cool" Message this is a developer debug message that should have been cleaned up before release, since it is not helpful for our users and is possibly confusing (“cool” can relate to temperature but that’s not what it means here 
) I will do this for the 25.4 release, replacing it with a more appropriate message like “Particle removed”, but this does not help the underlying problem of why the particles are being removed.
You are correct that “fluid time step” is the same thng as the main timestep (“Dt”). I’m not sure what else there is to try here. I’ll check with the developer of this code and see if I can find any further suggestions.