Polling for northern Maine missed by a substantial margin for pretty much every race on the ballot. It seems like this region is rather difficult to poll accurately, especially if Trump and/or Collins are on the ballot (there was also a large polling error in northern Maine in 2016, and Collins outperformed her polling average significantly in her two previous runs in 2008 and 2014).
Articles about polls in the Maine Senate race suggested that the race shifted significantly in Collins' favor during the final stretch (for example, one particular poll indicated that all undecided voters in that poll leaned toward Collins), and that people didn't expect Maine to be one of the few remaining places where split-ticket voters made up a significant chunk of the electorate.
Gideon also only won ME-01 by three points. She should have won it by at least 10. If she did, she would have pushed Collins under 50% and probably would have won with RCV. The ME-01 Collins/Biden voters were definitely gettable. They even voted for Hillary and Kerry for God’s sake.
