To be clear, I'm not counting the largely-hearsay-level charges in the filing as "documenting a serious problem": https://www.texasattorneygeneral.gov/sites/default/files/images/admin/2020/Press/SCOTUSFiling.pdf

It has such lovely gems as "Significantly, in Defendant States, Democrat voters voted by mail at two to three times the rate of Republicans." when as anyone who was half awake during the election knows, the Republicans were actively messaging their people to vote in person. And the gap was huge regardless of state: https://fivethirtyeight.com/features/what-absentee-voting-looked-like-in-all-50-states/

Trump even suggested double-voting as a hypothetical, as part of his attack on mail-in voting (as usual with NBC, it seems not to understand hypotheticals when it comes to Trump, but as President you have to be careful even with hypotheticals because some of your admirers also probably aren't very good with hypotheticals): https://www.nbcnews.com/politics/2020-election/trump-encourages-north-carolina-residents-vote-twice-test-mail-system-n1239140

And people were caught--Joan Marie Halstead, on your list.