I tried to figure out the specifics that would result in your exact situation, but without further information, I couldn't quite do it. However, I really think it might be resulting from you including a "File Open" or a "Save As" command (or both) in the action that your applies as it processes the images.
Because the batch process is designed to open an image, perform a specific action on that image, and then save the image with a specified name, in your situation, it seems as if it might be opening the same image over and over and renaming it.
You can check this by opening your Actions folder, and looking at the steps included in the action you are including in your batch process. If the first step is something like "Open" that is probably what is causing the problem.
I did a quick test using one of my User Created Actions inside a batch process with the same naming conventions that you used, and it seemed to work perfectly. Here is a picture of my actions panel--at the very bottom is the "Export as JPG" action. This is the one I used in my batch test.
This action is designed to open a high-resolution image, and resave it as a medium quality jpg. It was created for use on an open image, and you can see it begins with the "Save" command. Because it is using the "Save" command and not the "Save As" command, it captures the quality settings, but does not include any naming information, so it doesn't interfere with the Save As/Renaming function that is built into the Batch process.
You can check and see if there are any problematic commands in your action by opening up the action panel, and then clicking the down arrow on your action to show all of the steps. If you find a problematic step in the action, you can actually remove individual steps from an action by choosing the step, and then clicking on the garbage can at the bottom. That can save you from having to recreate your entire action.