Although state polls were wrong or within margin of error in 2016, in 2018, they were spot on with the house.
There is a reason polls do better with congressional elections than presidential ones.
Polls contact people who are willing to talk to them.
That is usually the most politically active folks who are far more likely to vote in Congressional elections.
It is apples and oranges—that is why many of the huge poll blunders in history have been in Presidential races.