WPT Creating a Lot of Instances on AWS

I’ve been running WPT on AWS successfully since last September or so. I have things configured to run agents in 9 different geographic regions and I have each region capped to 1 instance. Until recently, my monthly bill has been in the $500-$600 range.

However, I just happened to notice my AWS usage for the month of May is already up in the thousands of dollars! It seems things started going out of control around May 7 or May 8. As I look at my regions some of them have 15-20 instances running which means AWS has been billing me for thousands of hours of uptime.

Has anyone else experienced this? Has some recent WPT AMI update introduced a major bug such that 1) instances are no longer shut down when not in use and 2) instances are no longer reused?

Any insights would be greatly appreciated.