Hello,
Sorry to hear you are having issues. Look like the taskbar button is under never combine mode and it change from text visible to hide text on the taskbar buttons, this will happen when you have too many icons on your taskbar that text can no longer be available to be display properly. If you look at your first screenshot, there is at least one character still show up in the taskbar buttons but once you add one more button, the text might not show up properly at all, half a character probably, that is why, taskbar decide to hide the text, when that happen, it will remove lots of space previously for those text to show up. When this spaces added up, there will be empty space as you seen on your second screenshot. Which also provide space for more taskbar button. Hope I clear up enough for you.
Thank you.
Basj,
Stardock Community Assistant.