JS Error when editing menus

WP Multisite. When I try to edit a menu it does not update the subsites (again) and when I look in the Dev Console I see this error:

Uncaught (in promise) TypeError: Converting circular structure to JSON

--> starting at object with constructor 'Object'

| index 0 -> object with constructor 'Object'

--- property 'submenu' closes the circle

at JSON.stringify (<anonymous>)

at Proxy.saveMenu (menucreator.build.js?ver=3.4.02:1:5913)

at Proxy.n (menucreator.build.js?ver=3.4.02:1:5819)

at Proxy.returnMenu (menucreator.build.js?ver=3.4.02:1:13639)

at s.onClick.e.<computed>.e.<computed> (menucreator.build.js?ver=3.4.02:1:15867)

at dt (_plugin-vue_export-helper-D-PsXKsC.js:13:1373)

at He (_plugin-vue_export-helper-D-PsXKsC.js:13:1443)

at HTMLButtonElement.n (_plugin-vue_export-helper-D-PsXKsC.js:17:8220)Understand this error