The best way to see the problem is when "course recycle bin" is disabled. If enabled, the problem is delayed until the lifetime expires and then it will produce problems with cron running (records marked with "deletioninprogress = 1" in mdl_course_modules, records not being completed in "mdl_task_adhoc", etc.).

Problem:

1. Create new instance of BigBlueButton activity in any course.
2. First try to delete this BigBlueButton activity shows "error/cannotdeletemoduleinstance" as first annexed image. This BBB activity remains visible in the course.
3. Second try to delete the same BigBlueButton activity shows another error: "Can not find data record in database", but activity remains visible (it doesn't work, of course).
4. Third try ... same error.
5. Eventually, after some cron executions, the BBB activity is not more shown in the course.

Note: I have tested the same problem with multiple environments.

• Linux server with Apache2 + PHP 7.0 and PHP 7.2. (Moodle 3.1.16 and 3.5.4)
• Windows 10 PC with XAMPP 7.2.4. (Moodle 3.5.1)
• Moodlecloud free site (Moodle 3.6.2).