Comsol CPU usage drops to 0% and "crashes"

Hello everyone

I'm having trouble solving some models:

After a certain time solving (hours), Comsol just stops solving, and its CPU usage drops to zero, or close, when it normally sits around 60 %.

From there, I can't cancel the solver, as it does not respond.

And I can't close the program, because something (I guess it gets stuck somewhere, either in the solver or in trying to cancel the solver) is preventing it from closing.

I'm using Comsol 5.4, in Windows 10, latest version.

Anyone else has had this problem?

Thanks