Maples have a shallow root system and may be competing with the pachysandra for moisture and nutrients. I’d suggest broadcasting some gentle plant food over the pachysandra…Espoma Plant-tone would be my choice. You should also consider adding a thin (no more than an inch or so) layer of soil over the pachysandra to refresh it. This can be done by lightly sprinkling the soil from your shovel…not the easiest task but, id the pachysandra has been there a while, it could probably use a pick-me-up.