Export Date feature all of a sudden not working

I had always been able to go into CATEGORIES click a subcategory , then highlight “select all” then click “export selected” from the choose action drop down menu and then i would be taken to the export data page .

This all of the sudden stopped working for me today. Now when i click “export selected” it stats on the same page and all the items chosen are now unhighlighted.

I usually export 100’s of products per category which was never a problem.

I was experimenting and if i highlight to export 100 items or less it works fine.

But usually i have about 400-500 items per category.

This is odd as ive exporting up to 1,000 products at once with never a problem.

If anyone is able to help i would appreciate it.