Hello, I have my scenario in below steps: > I am member

Let us assume you belong to "TaskRun" group and some other group "XYZ" (it is possible to be a member of more groups). When the task is assigned, the tp!assignees property of the task is set. tp!assignees is of user or group type. In this example, it will be set to "Taskrun" group. Now, once you accept it, you "own" that task(and not the whole group "Taskrun" - although you can require that all the users of the assigned group should complete that task to put it in "Complete" state). Hence, the tp!owner property is set to your username. tp!owner is of user type. Also the value of tp!assignees will still not change. It will still be "Taskrun" even after you accept the task. Only the tp!owner changes after accepting the task.
Now, assume you are removed from "Taskrun" group. Naturally, you won't be the owner of that task anymore. The tp!owner will be set to blank again. But value of tp!assignee will still be "Taskrun" group. And since you are no longer in that group, you will get an error the next time when you try to access that task. The system will not try to change the original assignees of the task to any other group. The original assignee will still remain "TaskRun" group. But since you are not member of that group, it will give you error.
I hope this clarifies your question.

Let us assume you belong to "TaskRun" group and some other group "XYZ" (it is possible to be a member of more groups). When the task is assigned, the tp!assignees property of the task is set. tp!assignees is of user or group type. In this example, it will be set to "Taskrun" group. Now, once you accept it, you "own" that task(and not the whole group "Taskrun" - although you can require that all the users of the assigned group should complete that task to put it in "Complete" state). Hence, the tp!owner property is set to your username. tp!owner is of user type. Also the value of tp!assignees will still not change. It will still be "Taskrun" even after you accept the task. Only the tp!owner changes after accepting the task.
Now, assume you are removed from "Taskrun" group. Naturally, you won't be the owner of that task anymore. The tp!owner will be set to blank again. But value of tp!assignee will still be "Taskrun" group. And since you are no longer in that group, you will get an error the next time when you try to access that task. The system will not try to change the original assignees of the task to any other group. The original assignee will still remain "TaskRun" group. But since you are not member of that group, it will give you error.
I hope this clarifies your question.