There were plenty of complaints about irregularities before, during and after the vote, especially in swing states. Vote count monitoring was one of these problems mentioned, where Republican observers were allegedly denied close access to the counting by (Democratic) poll center "officials".
So bipartisan and careful monitoring was, reportedly, not always possible. Some of these complaints were heard in subsequent state senate hearings but it seems that was as far as they got. Some of those hearings were accessible on the internet at the time but it's hard to find much of anything like that anymore - just like everything else.
Swamp Rules. OK?