Menu items not found

my menu items are again and again randomly deleted. After I add my nav items again to the menu they are deleted after a couple days. I cant find anything in the log. I found online a post regarding this topic which referred to a plugin names „stealth ..“. I do not use this plugin.

Its hard to test, because I would break my site turning off plugins and would have to wait a couple days.

Any Idea? Have you heard of plugins causing this lately?

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