I have a form where user can enter search criteria and see the result. This is s

If I understand correctly, you have a start form in a process which is used as a search page. Is this the sole purpose of that process?

After search user can also update selected records from grid. but if they don't want to continue they can move away from the form to say a tab for Record.

You are getting that error because you are using formLayout in start form. Even though it is not recommended, you can use dashboardLayout instead, which will get rid of that error. You will also loose the nice layout of the buttons at the bottom of the form and will have to move them elsewhere within the interface.

Remember process is only instantiated after the start form is submitted so if user move away there is no process/task for them to go back to.

Hope this helps.