Don't know why but in Screen3.bky and Screen3.scm files screen name was set as Screen2 instead of correct Screen3. Edited files in aia and now it works
A simple - and probably faster - way / solution would be to copy the Screen3 in the Designer and paste it into a new ScreenX. Then only variables and procedures that have not been copied from Screen3 have to be placed in the Backpack and re-imported into ScreenX. Then delete Screen3.