I suspect the errors are from sites that have installed the apps earlier.
Log sharing is only enabled by default from 17 Aug
It will be helpful to suppress the error if the trigger site has yet to enable log sharing. It will be good to have a mechanism to alert the site admins to look at the error or to enable log sharing.
As Hua has suggested, you are likely not seeing the corresponding logs as the sites that are experiencing the errors have installed your app prior to the 17th of Aug so likely not sharing logs atm. You can click on the Invocation errors link (or use the 3 dot menu) to access the error details view. This will help you identify the sites with the highest number of errors. If your app is paid, you can access the emails of your active customers through the sales, licenses, and evaluation reports in the Marketplace. For example, when you navigate to Reports → Licenses, you should be able to click on the customer in question and there will be an (email) link. You can then contact your customers to ask them to enable log sharing.