Catch is trends show the downward trend for Republicans since July. Before then both chambers were a lock for Republicans, set to gain many seats in both at around a high of 90% chance each. But after, their lead kept falling and falling as the Dems' chances kept growing, up to now where what was supposed to be a complete rout in both is instead the Dems gaining Senate seats while the Reps only controlling the House on a razor thin margin.
The takeaway is that as time goes on the advantage slowly creeps towards the Dems, and with over 30 days left they'll likely close/increase their gaps towards an even more favorable outcome.