For context, this is because Adam Gregg decided to resign from being Lieutenant governor to become the CEO of the IA bankers association.
An interesting tidbit on Gregg’s wikipedia page is that Gregg clerked for Justice Mark Cady of the IA supreme court. Mark Cady, who died in 2019 was the author Varnum v. Brien (legalizing gay marriage in the state) and Planned Parenthood v. Reynolds which struck down the 72 abortion waiting period law passed in 2017.
I want to speculate about the intra-GOP politics at the Capitol, but honestly don’t have enough to go on beyond that.
This started happening after 2016 too - Trump immediately tanked his public approval by doing wacky shit that pissed everyone off and Democrats would massively over-perform in special elections as a result. Trump’s supporters don’t show up to special elections.