I really thought that I’d posted about this previously, but I couldn’t find the post, and it’s something that’s tripped me up a couple of times.
When building a UI policy in ServiceNow, if you want to be able to clear the variable value, then you need to build it to hide the variable.
Or to put it another way, never build a UI Policy Action that has the ‘Clear the Variable Value’ box checked and which also has ‘Visible’ set to false.
If you do that, then when the variable is shown, the system will clear the value of the variable, which is never what you want to happen. You want the system to clear the value of the variable when the variable is hidden.