I'd say google it, but we know google is unreliable. I got it from reports on a number of sites, Kentucky and Pennsylvania both reported vote flipping, where voting machines flipped votes as did others. Kentucky Governor Andy Beshear (D), who won by 5 points over his Republican challenger, Daniel Cameron, despite Republican candidates for Attorney General and Secretary of State winning by 15% – 21%. Not a common occurence. Cameron is highly regarded in KY, in fact was leading Beshear in the last polls before the election by a substantial amount (similar to the margin of victory for the other 2).
If I gave you a single source you would probably doubt it anyway, that's what most people who have to ask for a source generally do. The truth is out there, you just have to do what the rest of us do and let it in.