@moooonlighty Try installing the world into a clean user data folder. Move your entire Sims 3 folder out of Documents\Electronic Arts and onto your desktop, open the launcher to spawn a new folder, and download Roaring Heights from the store. Install it, but nothing else, and see whether it shows up in-game. Let me know either way. And if it does work, please quit, restart your computer, and test again, just to make sure it stays installed.
@moooonlighty There are a couple different approaches. If you don't have much store content, and it wouldn't be a problem to reinstall it, then go ahead and install your other store stuff into the new folder. It's best to install the content in small batches, no more than six items or so at a time—the launcher doesn't manage large amounts of data well. Worlds should be handled separately, not in a batch with everything else.
Check in-game to make sure your content is all present and working, then transfer your other content to the new folder from the old one. And of course if you have no other store content, you can start here. This is a list of everything in your Sims 3 user data folder, so you'll know what you'd want to transfer:
https://sims3.crinrict.com/en/2011/01/faq-user-files.html
If you have a lot of store stuff and don't want to have to reinstall everything, there's a different approach. First, ditch the new Sims 3 folder you created and put the old one back. Double-check the launcher to make sure Roaring Heights isn't listed as installed, and make sure there isn't a Roaring Heights file in InstalledWorlds or Downloads. (If you find any in either location, delete them.) You can also delete everything in Downlloads: once the content is installed through the launcher, those files become redundant.
Now move your existing Sims 3 folder back to your desktop. Open the launcher to create a clean folder, but this time, you need to move over a file from the old folder first. The file is called ccmerged.package and is in DCBackup, and it makes your premium store content work. The point is, it needs to be present when each premium item you own is installed, or that premium item won't work. Make a spare copy of this file, just in case. When your existing copy of ccmerged.package is in your new Sims 3 folder, you can install RH again.
If it installs properly, you're going to move ccmerged back to your old Sims 3 folder, and the new Roaring Heights .world file from InstalledWorlds as well. Additionally, you need to move the file labeled dcdb0.ebc from the new folder to the old one. However, you need to rename it first so that its number is one higher than the highest-numbered .dbc file in your old Sims 3 folder. So if your old folder has dcdb0 through dcdb4.ebc, the file from your new folder will be dcdb5.ebc. Note: For this purpose, you can ignore the files with the extension .dbc, which are installed custom content and are read separately.
When you've moved the three files over, you can delete the new Sims 3 folder and put the old one back, then check in-game to make sure RH still works.
This second roundabout approach may or may not work, and it's definitely less reliable than reinstalling all your store content. But if you have a lot of store stuff, it could save you enough time to be worth trying. If RH disappears again, then try the first method instead.
