freontwel The Store content worked fine on patch 1.69 for years before the EA App came along. That's not to say that it never disappeared, but what you've described was relatively rare absent other system issues. It's still not common, just more common than in the Origin days.
Anyway, the next time this happens, try deleting the SigsCache folder instead. If that doesn't help, empty DCBackup as well as DCCache before reinstalling the Store content. I would also suggest installing the content into a fresh Sims 3 folder, and keeping a copy of this folder on hand so you can restore it if and when the Store content disappears yet again. It's easy enough to move your saves and other user content to the new folder.
Finally, when installing Store content, make sure the individual .ebc files in DCCache don't get much larger than 200 MB (204,800 KB). A bit over is fine, but something in the range of 230-250 MB may corrupt. The technique here is to install one world first, then progressively smaller sets until the files gets over the 200 MB line, at which point the launcher will create a new .ebc file the next time you install anything. Then you install another world, then sets, then smaller sets, rinse and repeat.
