I have a user with tasks assigned to them who has not been able to open her tasks. First she can't see her tasks under her tasks view or the available view. But she has been finding them under My History, Involving Me Search. She can then open the instance details and see that they are assigned to her.

In actuality it has been re-assigned but she can't see this until she click Open Task. Then she gets this message.

Her login shows that she is logged into the correct user account.

From my administrative instance monitoring view I can see that the last status of the task was being assigned to her but no details about the re-assignment.

When I re-assign it to her as an administrator it doesn't make any difference. The only option we could find was for me to re-assign it to someone else temporarily and then back to her, then she could click open task and access the task AND it would show in her task view.

Since I can't see who these are getting re-assigned to or how they are getting re-assigned I can't think of any way to help.