You have a task that is repeatedly crashing and is being restarted.
Each restart creates a new taskbar icon but the old one isn't removed as the task ended with a bang. When you click the caret to show the icons, the taskbar refreshes and so clears the old icons.
When I had this problem, I found the culprit by looking in the Event Viewer logs for task terminations due to error. This may work in your case and that may give you a clue.