If you're looking today specifically, it's "Schedule Change Saturday" and sometimes fares do wonky things as the new schedules are being loaded. Give it a day or two and see if the fares normalize to what you were previously seeing again.

That said, if you've been looking for a little while and noticing this, then the case is more likely to be that that's what the fares are. If fares seem expensive you have a few options:
1) Hold off booking to see if fares drop as DL will adjust fares based on actual demand versus expected demand and remaining supply. Of course this carries the risk that the ticket prices could go up more
2) Book now but continue to monitor fares. If fares drop, rebook and get an ecredit for the difference, if you'll be able to use the ecredit for another DL flight down the road
3) Look at other airlines for all or part of your trip
4) Instead of booking CDG-Stopover-GRU and GRU-Stopover-CDG, see if a series of one-way tickets or if two open jaw (CDG-XXX//YYY-CDG and XXX-GRU-YYY) or two round-trip tickets at the same stopover city are priced more favorably.