Process instance execution transaction


I’m trying to get the process instance state based on REST api. I could search for execution and activity ID but it seems to have some transactional issue: When I start the process (start event → parallel gateway to execute 2 service task → join → service task → end event), I always got the activity Id linked to the start event, until the process ends: no more execution with an activity ID).

Is this a normal behaviour? Is this the right way to get process instance state?