This is for an on-prem Sharepoint 2010 workflow. Migration underway to SPO but still have a couple left on old system. My workflow has a state machine.

One of the states has a parallel action. One side waits until 6 questions have been answered on form, the other side has a task assigned to the user. Once all the fields are answered it's supposed to auto complete the task. It seems to fail here a lot, but not all the time. I cannot figure out why. 

The only error displayed is “an error has occurred”. The log files don’t give me anything different. Any idea why this is?