It seems like there might be some compatibility issues or changes in the Angular framework that are causing the error after the update. The error message suggests that the formGroup property is undefined in one of your custom modules.
Here are some steps you can take to identify and fix the issue:
1. Check Angular Version Compatibility: Ensure that your custom modules are compatible with the Angular version 8.4.2. Sometimes, updates may introduce breaking changes or deprecate certain features. 2. Review Changelog and Release Notes: Look into the Angular release notes and changelog for versions 8.2 and 8.4.2. Check if there are any breaking changes or updates related to form groups or other relevant features. 3. Examine Your Custom Module Code: Inspect the code of your custom modules, specifically the part where the error is occurring (e.g., in the cE function). Look for any usage of the formGroup property and ensure that it is properly defined. 4. Update Dependencies: Check if there are any third-party dependencies or libraries that your custom modules rely on. Make sure that they are also updated to versions compatible with Angular 8.4.2.