Queue does not process

I did a fresh install and was able to process the queue for testing campaigns all I wanted. Then out of the blue, when I was trying to send a test out and when I click on Process Queue to manually process, it just sits at the screen with the spinning circle and the Stop Processing button.
It sat there like that over night and was timed out in the morning. If I click on Stop Processing, and then try to process it again it gives me the text that another process has been running and it is going to sleep for 20 seconds.

I’ve done no manual configurations to my install, this is a stock install from my host.

I might have this one figured out. I had the Subject Line Place Holders plugin installed. When I disabled it, it looks like the queue may be processing now. I’ll check back if it sends the message out.

EDIT:

Correction, after turning plugins back on and then off one at a time, it was the AutoResponders plugin that was causing the issue.