http://download.macromedia.com/pub/developer/aftereffects/scripting/JavaScript-Tools-Guide-CC.pdf
About ScriptUI before CC 2015 there were reported bugs in ScriptUI Adobe did not fix great users like Paul left here. In CC 2015 Adobe replace ScriptUI with a new implementation of the the interface. Support for some files types were dropped which broke old working scripts. Other features were dropped so dialog old script positioned dialogs are now centered. Other feathuresrs were not implemented well so some old script may have problems. Code does not get executed that controlled what data could be enter into dialog. So user errors can now be entered in fields that have code to prevent invalid data types from being entered. So incorrect user input can cause scripts to break.
Hopefully Adobe will fix Bugs some day. Adobe has claimed they fixed the bug in the first and second CC 2015 updates. The Bug has not been fixed.
Photoshop CC 2015: Scripting addEventListener keydown event not working
Other ScriptUI bugs have also been reported.