I am using WordPress

Jupiter theme version 1.0

WordPress version is

4.7.15

Mega menu option was enabled for some menu items and it was working perfectly for years.
But suddenly from several weeks ago, mega menu was disappeared. Even the checkbox to enable that feature also not available.
As a quick fix, I restored a several weeks old backup.
The restored site had the mega menu, but after several hours it was gone again.
What may be the reason for this behaviour?
How can I get mega menu back?