When I type double underscores in the Frontmatter as a value with Metadata Plugin, it disappear all notes in my vault completely if I open them!!! But the files in the Datatree displayes correctly!
I opend some MD Files within this Vault and the Plaintexts in these Files also still there.
I found out that the Dataview Plugin makes that trouble, when I delete all the plugins localy and installed step by step the deleted plugins.
I escaped the double underscores with the escape character
Now, the Dataview worked fine
I used these additional plugins
I’m really sorry that I cannot dive deeply in my (hopefully) solved problem to inform you better. Anyway I hope it is in that case clear so far