I can not share Tasks - Attach details of the Error

I can not share Tasks - Attach details of the Error

I user1 have several Tasks created and with Sub-Tasks. When I add a user2 to a Sub-task

User2 receives a notification that I shared a Task, without informing that it is actually a sub-task. Then it clicks and displays a message "Operation Not Allowed"

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Then I, instead of sharing the sub-task, added user2 to the Task.

User2 receives a notification that I shared a Task, can open a window, but does not show all the texts, can not read anything inside, has no clickable options.

What to do?