@puzzlezaddictHi there, @Pandorax4 is completely correct. The Pop Up sale you're referring to which ended on Feb 9 had sales on Expansion and Game Packs, but no Stuff packs at all were for sale. I was close to buying a few packs in Steam for the 25% off/ 7.49 price, which began about the time the Exp packs/ Game packs Origin sale ended. I own Sims 4 through Origin, Xbox and Steam, but now play through Steam. We're able for the PC version, as long as we own the base game in Steam to buy our DLC wherever is cheapest (Steam, Origin, or stores selling DLC codes like Amazon, only XBOX is separate) and it installs to our game.
I can confirm this was an entirely new sale, which specifically has 50% the Stuff packs branded all over in game including banners on the Gallery circle icons that states 50%. This is still active now and has been active for the past couple days. I thought maybe it was in preparation for the Lunar New Year Sale and now there are some items on Sale in Origin, but not the Stuff packs. But it remains in game when you click Buy Now it links us to Steam and adds it to our cart for 7.49. I indeed cleared cache multiple times the past couple of days for Origin, the Sims folders including spotlight cache, etc. and even the 'download cache' in Steam.
The main difference is that the 4.99 price is incentivizing me to pretty much buy the remaining stuff packs I was missing versus planning to hold off until the anniversary sale like they had last year. I contacted Steam support and all I got back was we don't price match. I've responded to them now and said wasn't looking for matching, but we are just trying to understand where this sale is meant to be on which site. Thanks!