I am doing same but i have encountered another error, as your diagram i have created a similiar one, but my task8 which is a service task is not moving forward.Paralleltest2.bpmn (6.6 KB)
In my BPMN this task8 is of name Change_variables.
Everything seems ok, in my point of view. You have to check external tasks logs and maybe model consists some other errors so rollback innitiated to async save points.
I have checked the external task the error was in it but no error is logged, i resolved it is occuring because i was doing
//const variables = task.variables;
//processVariables.set(“name”, ‘vineet’);
by elemenating these lines error is resolved, but no error was logged in external task