Thanks for contacting WHMCS! The reason you receive the Module not found error is because no module is assigned to the product/service. WHMCS is designed to attempt to run a function once a service is renewed and because there is no module, there is no function. More information: https://docs.whmcs.com/Provisioning_Issues#Required_Product_Module_.27.27_Missing
We really recommend setting these products up to use the AutoRelease module. This ensures that WHMCS has a module to work with, even if no action is required.
Some logic was updated in v7.6 that resulted in this error now being fully logged, however this has been documented and suggested for quite some time.