Process Definition is not working with assigned user and change field actions

Hi All,

I am trying to create one  process definition with actions assigned user( to assign one user) and change field ( to update team) based on condition which I mentioned in start for newly created records. But when I enable that process definition after creating a new record I am getting 500 internal error, if I remove the assigned user and change field actions fields I am not getting any error.

Once the record is created team is updating but assigned user is not updating (and also not able to see in process management) but in view audit log I can see the new assigned user value. 

Does anyone have idea on it?