When files are missing from the TSR Custom Content Manager, there can be a variety of causes...
1. The game is running when you try installing the content
Make sure the game is not already running when using the TSR CC manager (both access the same files and that can lead to conflicts and crashes). Also, ensure you close the TSR CC Manager before starting your game. That way, there will never be any file conflicts.
2. A utility is preventing your files from downloading
Various firewalls, anti-virus tools, and proxy software have been found to trap files. You will need to ensure that, if you have such programs, they are not blocking your content. One way to achieve this is to look for a "safe list" (sometimes called a whitelist) for website addresses and applications. Make sure the TSR CC Manager (typically found here: C:\Users\[YourName]\AppData\Local\Programs\tsr-manager) is added to all safe lists, and also add our site (www.thesimsresource.com).
Known applications that cause problems include AVG's pop-up blocker, Ad Blocker Plus (even if our site is marked as allowed), and Avast's Ransomeware Shield where the CC Manager will need to be added as a safe application.
3. Your browser settings might be preventing zip downloads
Check your browser security settings aren't too high. Google made a recent change to Chrome that now seems to treat all zipped files as insecure files (all our sets and larger downloads are in zipped files). To test if this is an issue, go to our site and download a set of objects (you don't have to keep them - this is just to test a larger zip file with multiple contents). DON'T download with the TSR CC Manager - just use the normal download button. Do you get any browser warnings? If so, you need to lower the restrictions of your browser to let zip files through (look up your browser's support page online if unsure how to do that).
4. Something is locking the files, preventing installation
If you use Onedrive, Dropbox, or any other utility (such as backup software) that might try to take hold of the file at the same time the TSR CC Manager is trying to install it, the two will clash, and your file might not install correctly or at all. This will lead to missing files or the "Corrupt Database" error in your log.
5. The downloads need other files installed
A less likely possibility is that the downloads you're acquiring might be dependent on other files. This can happen when downloading Sims, lots, hair, or object recolor sets. For the problematic items, it will be worth revisiting the download page to ensure that you do have their required files installed first. If you have VIP membership, you can download any newer content (submitted from October 2020 onwards) with all its required content in a single download!
6. You're missing the resource.cfg file (or lines are missing)
If you have content in sub-folders but have removed your resource.cfg file (found in the Documents/Electronic Arts/The Sims 4/Mods folder), then your content won't show in the game. Make sure your resource.cfg file shows these lines (note that the first two lines are only needed if you use TSR CC Manager):
Priority 490
PackedFile TSRLibrary/tsrarchive*.package
Priority 500
PackedFile *.package
PackedFile */*.package
PackedFile */*/*.package
PackedFile */*/*/*.package
PackedFile */*/*/*/*.package
PackedFile */*/*/*/*/*.package
Note that the first two lines will only be needed if you use the TSR CC Manager. The lines starting Priority 500 onwards are mandatory.