If you’re using a cookie consent form, Google Analytics won’t record a visitor until they opt-in. Depending on the design of your consent form, this number can be anywhere from 10-90% of your visitors.
On the other hand, Independent Analytics does not use cookies, nor does it store personally identifiable information, so it does not require visitor consent before tracking. This means that 100% of the visitors get tracked. This can lead to much larger visitor counts than seen with GA.
First, Independent Analytics does not track AMP pages, so you will see more visitors in GA if you are using AMP on your site.
Next, make sure that you have cleared your cache after installing IA. The cache needs to be cleared once so that the tracking script can appear on every page of the website.
Lastly, check if the Google Analytics script has been added more than once. It is easy to make this mistake if you end up with multiple plugins or custom scripts adding the tracking code to your site.
Those are the known reasons why you may see a difference between stats in IA vs. GA, but if none of those explanations fit your website, feel free to reach out to support@independentwp.com, and we can debug your site for any potential tracking issues.