I can see that this is a common question and I want to help you all come to a resolution. I did some further research on my end and if your product prices aren't updating on your Instagram products after performing the previously mentioned troubleshooting steps, then I would recommend connecting with Facebook Support. They may be able to help you with some product tagging errors, which sound related to what you are experiencing. You can chat with them here: Facebook Live Support.
Sometimes the chat may not be available, if you run into this, you may also try their Commerce Support Form, here. You'll need to be logged in to your Facebook Business Manager to view this.
Let me know if this helps!