In particular this case: A plugin was not properly uninstalled from the site

LMS/web: users can still use the Moodle site without problems

App/ws: users are blocked, they see the following exception:

Coding error: version.php file is missing for the component X

This is also happening when retrieving courses (cannotgetcoursecontents error) when they configured course formats that were uninstalled (lms defaults to topics in this case)

STEPS TO REPRODUCE:

• Install a course format that add WebServices to the mobile app service (format_wplist for example) and then uninstall it just by removing the files (and not executing the plugin uninstall code)
• Try to access the site using the mobile app, you'll receive an exception
• Install a course format plugin, configure a course to use it, and then uninstall it just by removing the files (and not executing the plugin uninstall code)
• Try to access the course using the mobile app with a user enrolled in it, you'll get an exception. Or call the Webservices core_course_get_contents and core_webservice_get_site_info to get the exception