Here are some common reasons that your feed may not be updating or takes longer to update than the time you have specified in the “check for new posts every” setting.
1) Your access token has expired
If a feed is not updating at all, a backup feed may be in use due to the associated access token expiring. This is more common with access tokens from personal accounts. Instagram will invalidate access tokens at random times without warning. Refresh the token by clicking the big blue button on the “Configure” tab.
2) You are using a caching plugin or your server may have a caching system
Since version 2.0 of the free plugin and 5.0 of the Pro plugin the HTML for the feed is loaded along with the rest of the page which means it will be captured in a page cache. You can workaround this issue and have the feed update more often by enabling the setting “Load initial posts with AJAX” found on the “Customize” tab, “Advanced” sub-tab.
3) Your database does not delete temporary data (transients) as expected
There are a small percentage of WordPress sites that do not clear what are called “transients” in the options table of your database. To workaround this issue, you can enable the setting “Force cache to clear on interval” to delete the transients with a manual MySQL query on an interval.