That the task was assigned correctly to all 3 users. We can see that in the Participant section of the view flow.
The problem can be potentially related with user accounts. As I can see, that the task was assigned to K2SQL accounts. It means that you are using SQLUM identity. I would suggest you to double-check that users are using their SQLUM account for authentication. They should use form authentication in this case.
In case if you don’t want to assign task to SQLUM users and it happens automatically, I would suggest you to assign a task using user FQN. Instead of searching user and providing display as an input, just provide string in an FQN format (i.e. K2:DomainName\UserLogin). I would also suggest you to use the same approach with FQN for assigning tasks to SQLUM users.