Jobs remain in unwarranted "waiting for parallel" status.
The relevant job object has max parallel = 1, and five of the jobs have completed, but the remaining instances stay in "waiting for parallel."
Either "release manually" or "ignore agent resource" on a waiting job will cause the engine to re-evaluate the situation, and the job will start.
Release : 12.x
Component : AUTOMATION ENGINE
Update to a fix version listed below or a newer version if available.
Automation.Engine 12.1.9 - Available
Automation.Engine 12.2.7 - Available
Automation.Engine 12.3.4 - Available
A problem has been fixed where a workflow was blocked by false "Waiting for parallel" status.
This problem occurred sporadically when finished tasks that had post-condition check on a task inside the workflow were wrongly taken into consideration.