Steps to reproduce the issue

Having a Menu structure like this:

Menuitem (Article)

• Subitem A
• Subitem B
• Subitem C
• Subitem D

I was lazy and wanted to copy Menuitem as a child of Menuitem to transform it later into an Alias like that:

Menuitem (Alias)

• Menuitem (Article)
• Subitem A
• Subitem B
• Subitem C
• Subitem D

So I ticked the checkbox only in front of Menuitem and made a batch copy with destination Menuitem.
The result was unfortunately this:

Menuitem (Article)

• Subitem A
• Subitem B
• Subitem C
• Subitem D
• Menuitem (Article)
• • Subitem A
• • Subitem B
• • Subitem C
• • Subitem D

Ok, so my lazy way did not work and i ticked the checkbox in front of the third level items and clicked on trash.

The result:

(no more Menuitems)

All items were deleted not only the new copied Menuitem inside the Menuitem.

So i went into the trash to restore the originals. But restoring is not possible.

So i thought about deleting half of the items, to be able to restore them then but then I get following error:

System information (as much as possible)

Joomla 3.7.4

Additional comments

By trying to rebuild the submenu items suddenly my whole menu dissapeared :( There is something massively broken, restoring the items that i never trashed failed.

I tried to reproduce on a clean install and unfortunately could not reproduce there.