Task stuck at node and not moving ahead without throwing error.

I was debugging a task and found that the task was stuck at a node without any errors or alerts .

There was nothing wrong in the process from where I was calling it. 

There was clean up done for the environment recently, exactly two days ago.

Later on checking the logs, found this error :

10:24:50,053 INFO [stdout] (Appian WorkPoller - 2 [Notifications] (originally: default-threads - 5)) 2017-11-24 10:24:50,053 [Appian WorkPoller - 2 [Notifications] (originally: default-threads - 5)] ERROR com.appiancorp.ra.workpoller.WorkPoller - Could not obtain 3 thread(s) after 4400000 attempts in work poller
10:24:50,357 INFO [stdout] (Appian WorkPoller - 1 [ProcessExec01] (originally: default-threads - 4)) 2017-11-24 10:24:50,357 [Appian WorkPoller - 1 [ProcessExec01] (originally: default-threads - 4)] ERROR com.appiancorp.ra.workpoller.WorkPoller - Could not obtain 3 thread(s) after 4400000 attempts in work poller
10:24:50,455 INFO [stdout] (Appian WorkPoller - 4 [Collaboration] (originally: default-threads - 6)) 2017-11-24 10:24:50,455 [Appian WorkPoller - 4 [Collaboration] (originally: default-threads - 6)] ERROR com.appiancorp.ra.workpoller.WorkPoller - Could not obtain 3 thread(s) after 4400000 attempts in work poller
10:24:50,785 INFO [stdout] (Appian WorkPoller - 5 [ProcessDesign] (originally: default-threads - 7)) 2017-11-24 10:24:50,785 [Appian WorkPoller - 5 [ProcessDesign] (originally: default-threads - 7)] ERROR com.appiancorp.ra.workpoller.WorkPoller - Could not obtain 3 thread(s) after 4400000 attempts in work poller
10:24:51,134 INFO [stdout] (Appian WorkPoller - 3 [ProcessExec02] (originally: default-threads - 2)) 2017-11-24 10:24:51,134 [Appian WorkPoller - 3 [ProcessExec02] (originally: default-threads - 2)] ERROR com.appiancorp.ra.workpoller.WorkPoller - Could not obtain 3 thread(s) after 4400000 attempts in work poller
10:24:51,587 INFO [stdout] (Appian WorkPoller - 6 [ProcessExec00] (originally: default-threads - 8)) 2017-11-24 10:24:51,587 [Appian WorkPoller - 6 [ProcessExec00] (originally: default-threads - 8)] ERROR com.appiancorp.ra.workpoller.WorkPoller - Could not obtain 3 thread(s) after 4400000 attempts in work poller

Can somebody please guide how to resolve this issue.

This still persist even after a clean up.

Looks like its certainly a server issue.