Try temporarily inactivating this script to see if the behavior is the same.  It sounds like you have another Catalog Client Script or UI Policy affecting this variable.  Since it's after after an update, it could also be a Client Script, UI Policy, or Business Rule on the sc_task table.  In the script, you don't need variables. in g_form methods.  It's probably not hurting anything as long as it is otherwise working, but it is unnecessary. 

Hi Brad,

My requirement is to make some variables mandatory & visible when catalog task short description is something something . 

When I am writing Onload client script to make mandatory and display true based on short description. After saving the from its clearing the value from the form

When I am writing Onload client script to make 

I was following that, but the cause may be a different script is why I suggested trying to make the variable visible if it's not already, then trying the same test steps with this script inactive to see if the same behaviour is observed.

Hi Brad ,

I deactivated the script its working fine as expected but the hide and show of variables based on short description is not working all the variables are visible on all the catalog task form 

Thanks for confirming that.  So only with this script activated, which is only controlling the mandatory and visibility of two variables, when you select a choice on one of the variables and save/submit, the value is missing when the form reloads?