You just can’t trust the polls, especially the generic ballot polls. I’m curious which polls you see that worry the most, I’d like to see the internals. It’s easy if you oversample NY and CA to slant the numbers - even likely voter numbers - obviously because those states lean harder to the left.
But all politics is local (remember the good old days, compared to today when Democrats like Tip O’Neil looked level headed?). Each House race has to be polled on its own, and the politicians have their private polling outfits giving them the scoop - small sample sizes can sometimes get you lopsided results, that’s just statistics, but they can also be confirmatory if you are getting consistent numbers or numbers large enough outside the margin of error).
Real clear politics current projection for the house:
205 dems, 199 republicans, 31 tossups.
https://www.realclearpolitics.com/epolls/2018/house/2018_elections_house_map.html
538 blogs projection:
https://projects.fivethirtyeight.com/2018-midterm-election-forecast/house/