The Republican governor of Missouri signed a law in June allowing people receiving mail-only ballots to return them in person, as some voters prefer dropping off ballots instead of standing in line during COVID. It required signature validation. A liberal group sued, and won at the appeals level. Now people who have thought since June that they could hand drop their votes are subject to the whims and inefficiencies of the US Postal Service.
Source: Voters who want to vote in person forced to use Postal Service