Home Menu and Submenu’s qty problem

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I want to create my own structure on home menu and submenu’s, it worked so far but when i add some categories automatically eliminate the others (i think from bottom to top).
Trying to explain a little more here… i count 90 in total, menus and submenues. If i add one more at bottom (would be number 91) it wont save it, and if i add one in the middle, the one that is at bottom will be eliminated. Its possible that theres a limit of 90? how can i remove it, or extend it?
PS: im NOT familiar with any of this stuff.

thanks in advance