Make sure you're using:

xPopupArrowFontAlign right

The arrow (fonts) aligns left by default, and could be hidden under icons or your folder texts.

You'll also want to play with these two settings, so your folder text doesn't overlap the arrow:

xPopupEntryFontRightBorder #
xPopupArrowFontRightBorder #

Lastly, the arrow is black by default, so you may also want to throw in:

xPopupArrowFontColor ######

(# = some value)