query_var suddenly returning blank string

All forms are effected.
There is a field on every form that is populated using query_var(event_date) where the event_date is a parm in the url. This is suddenly not picking up the url parm and instead is populating the field with a blank.
PH debug does not show any errors in the log file.
Any advice on how to resolve?

The plugin is “WS Form Lite” Version 1.10.86 and WordPress is Version 6.9.4