Green stoll is usually from bile. If it hasn't had eough time to break down and turn brown.
pantoprazole is a proton pump inhibitor. Reduces acid in the stomach. It's for like acid reflux disease and hiatal hernia.
GERD has been linked to gallstones though not conclusively. It could be the bile is flowing normally again but there could be a lack of microbes (probiotics) to break the bile down or moving through the large intestines too fast.
It could also be Malabsorption or bacterial overgrowth, but you arn't feeling ill right?
Sounds like you may have an infection of some sort.
Best thing to do is go to your doctor..eve if you have to talk poo again :) Good thig is ..seems like you have your IBS mostly under control.
Be well