often I happen to remain lines on the surfaces in correspondence of replace face or boolean carried out under tangency conditions. There is a command that allows me to "clean" the surface from those curves I attach an example image.
the only one that can work in the case of the first arrow at the top is optimize face. but shoots everything, at this stage I cannot use it. the various replace, delete and make coplanar face I have already tried them but not always solve the problem and however can be used only in the case of 2 distinct faces and not in the case of lines that soil the surface. . .