Intermittent errors similar to the following occur on user tasks that contain a boundary event.

An issue occurs where the related task or parent process is no longer in the act_ru_execution tracking table when both of the following are true:

• The task is within the range of the event expiring.
• Another user also updated this process.

The Flowable library itself handles this update. 

Workaround

The hot fix for this issue includes enhanced error messages.