Dear crafte,
Thank you for your reply.
Below please find two scenarios I am experiencing.
1) After the teacher role is removed from the user who has missing To Do items, the missing To Do items reappear in his To Do list. The course in which the user was assigned a teacher role is different from the course with missing To Do items.
As shown below, there are only 5 To Do items on the left (with teacher role) that the items highlighted on the right are missing.
[picture removed]
2) I compared this teacher user's To Do lists in both the production site and testing site and found that Student To Do items are missing from the production site. Please see below screenshots for your reference.
[picture removed]
Your assistance to these issues will be much appreciated.