Script Task Unattended forever

Hi,

We have a script one query entity rule which is working fine if we execute that in rule editor , but if call the same rule in Process model Script task is showing unattended and it not executing. its only happening for this query entity 

Also we are getting below error after some time in logs 

ERROR com.appiancorp.ra.workpoller.WorkPoller - Could not obtain 3 thread(s) after 1840000 attempts in work poller

Thanks

Ajinkya