both in state AND federal court. The feds generally wave it away Because. State. Issue. But the GOP keeps going there anyway because the state Supreme court is majority (D). The state Supreme Court keeps punting when they end up having to decide, and it seems to always happen just ahead of an election so they leave it "as is".
During that time as it was being adjudicated and was in effect, Democrats HAVE been doing massive education campaigns and ads and redesigning and redesigning again, the envelopes (to the point of actually pre-filling out the YEAR boxes). But because our urban areas ARE diverse, with many nationalities and languages, there is still confusion. Here was Philly's last year -

You have procrastinators who often hurry their way through the ballot and shove the completed ballot directly into the "outer envelope" (forgetting to put it in the "secrecy envelope" first (making that ballot a "naked ballot" )) and then forgetting to sign/date that outer envelope, just to get it in the mail or at a drop box in time.