I read some postings about a very bad smell when cooking certain meats. I am just beginning to use my Instant Pot, and I have noticed this myself. Here is one suggestion: never use a butter-flavored pan spray in the inner pot. These contain buteric acid and I believe that this can cause the odor. Also, make sure not to overcook the meat, which breaks down certain proteins and emits noxious gasses.
Set your cooking time based on the type of meat and weight of the batch.
I never had this problem with a slow cooker, and I believe that the higher cooking temperature makes strange things happen.