On May 22, Chris Getty, an independent candidate for U.S. House in Illinois, submitted almost 20,000 signatures to meet a requirement of 10,816. See this story. He is running in the 4th district, where the incumbent Democrat did not run for re-election, but he didn’t tell anyone he wasn’t running for re-election except that he tipped off his campaign manager. So she submitted a primary petition and became the Democratic nominee by default. If other Democrats had known the incumbent wasn’t running for re-election, there would have been many Democrats running for the seat.
Getty is personally a Democrat, but Illinois does not have registration by party.