We'll see a lot of new voters this cycle - people who usually sit out midterms, maybe newly-enfrachised people with felonies on their records, or people who never vote but have finally had enough. I'm not a statistician, but I imagine those folks might not be captured by standard polls.
Nate Silver saying there is an increased chance of polling considerably underestimating Dems: @hydevoltyge.bsky.social utter vindication