“I personally know a prominent Chabad Mohel who declined to do the bris of a the child of a very famous and wealthy couple where the wife was a Giyores of a frum Beis Din, because a concerns about the Kabolas HaMitzvos, or the lack of it.”
Another excellent point drawing attention to another example of goyim R”L mixing into Klal Yisroel. Even purported “geirim” of so-called “Orthodox” beit dins are often fake converts.
This, too, is very common.
“regarding “Mihu Yehudi”, and the concern of Goyim in Eretz Yisroel being considered Jews under the Law of Return”
And yet another example of goyim pretending to be Jews. This time in Eretz Yisroel. And literally numbering in the hundreds of thousands when considering the fake conversions the Israeli rabbanut recognizes among the Russian gentiles in the state.
“Once, I was being Mesader Kiddushin, and under the Chuppa I discovered that the Chosson was not in fact a Yid, and I was saved from making a Bracha Levatala R”L…”
Another all-too-common scenario. More often than not it isn’t stopped in time and remains unrecognized r”l.