some of the field display blank in prodroute form

Why are you trying to replicate it if you no longer have it? Look at your route import routine and look at the tables and how these are mapped, look for the operation number, if you have source format blank the operation number and import it.

You leave the empty field by not populating it in the import and seeing if it imports. Do you create base routes through an import routine?

This issue occurs frequently for after some days .I want to know how come this issue might occurs in past.

From where its generating and how it generated

At the very start a route is created against an item. How is the route created? It is generated from the data in AX.

I have replicated the issue.when the status of the batch order “Estimated” then blank records is created.can you suggest me to possible solution

Firstly post a picture of the route against the batch order with blanks, and then against the released item on the batch order so we can see them.

I unable to get can you explain me more.Which class is responsible to create the blank records.

No class.
It is poor data.
I will assume you import your routes with incorrect validation creating blanks.
You have said it is not an issue now so someone has corrected the data. So you cannot reproduce it.
Analyse your import routine and the data being used.

Now I have reproduced the issue with blank records,but i am not able to find out how its blank record is created.Can you suggest me

Have a developer to debug. May be by adding a break point to ProdRoute.insert().

Check the route against the released product!!!