This is one of the issues outstanding long time. What’s the cause? I guess, Katalon Studio turns a script of Test Case in Script mode into Manual mode, then later it turns the script from the Manual mode back into the Script mode. Unfortunately the code transformation from the Manual mode to the Script mode seem to have some bugs. I guess there might be some technical issues in Groovy, Eclipse or Java which make the issue unable to fix. Especially I have a doubt that the Abstract Syntax Tree Transformation of the Groovy 2.4.x could have some bugs. As you may be aware, Katalon Studio uses very old version of Groovy, Eclipse, Java. If there is any problem in the base layer that blocks Katalon developers, they must starts with overhauling their product.
By the way, just recently @duyluong made a comment in another post in the Katalon forum:
He suggested that Katalon developers are trying to overhaul Katalon Studio at the moment. This must be a big news to us, Katalon users. But we all know, any changes at the base layer may cause new problems. Users should wait and see if the Katalon team could manage it.