Why button "Change <--> Display" on dataview disappear?

Hi Sap Gurus,

I am facing with a strange issue:

Usually, on dataview, we can find button "Change <--> Display (Ctrl + F2)":

Button sometime, this button disappears automatically. And after someday, it appears again.

Currently, it disappears and customers can not do anything:

What is the cause? How can I fix now?

Thanks very much for your kindly help.

Duyennx