Just FYI for anyone googling for a reason for symptoms: This bug (i.e., rawtherapee 4.2.1241 is incompatible with GTK 3.22) also makes the rawtherapee exposure tone curve widgets unusable: they don't refresh properly, so the curves become unreadable.
Best to downgrade to 4.2.0 until support for GTK 3.22 is added
