Typically, in-person ballots get reported before mail-in ballots are reported. It's sometimes also the case that ballots cast on election day get counted before ballots cast at advance polls.
In past elections, many Republican-controlled areas have seen voter suppression at in-person polls in heavily Democrat areas: e.g. understaffed polling places, leading to very long lines for voters.
This election, there was a concerted attempt by many Democrats to do an end run around these suppression tactics by voting by mail or voting in advance polls. Because of this, the early results in many areas skewed Republican until all the votes were counted.
Is that what you're describing?