I have canned for years. Tomatoes, jams, etc. I startedcanning my own chicken broth and sometimes it spoils or smells terrible after canning, even though it seals. It's usually no ore than a few months old when I try to use it, but am disappointed when I open it and it smells too bad to use. Sometimes it's good, but a lot of times not.why?
If it's spoiling frequently, you're using an unsafe process. (Maybe boiling water bath, no pressure?) That means you should not eat anything else you've canned with the same process, because it could've become dangerously contaminated without obvious signs.
The only safe way to can low acid foods is with pressure canning. You should precisely follow a recipe from a trusted source, like this meat stock recipe from the NCHFP.