The history between May and August was deleted on Redfin. Either there is a way to pay Redfin to delete history or @lotsofpulp is right, or maybe a convenient bug?
Yeah that's a trick. They take it off the market and then relist which resets the clock. They do this so buyers won't assume there is something wrong with the property due to the price changes.
I might be wrong and have just looked at a couple houses where the data is missing now. I set the Zillow filter to “price reductions”, which Redfin does not have, but I compared a few homes and both listed price changes.
The houses I had favorited with the missing price changes are gone from my Redfin favorites list now (owner decided to remove listing?).
Zillow definitely has better history though, and a filter option to show price reductions.