try giving them a dose of epsom salts. the yellowing is often a sign of magnesium deficency so Magnesium sulphate should help green them up again. dont over lime them.
Pachysandra is a good plant for deep shade so perhaps the ones in the full sun were damaged by the light intensity.

I know that Pachysandra turns yellow when waterlogged. I had a similar problem in the past. My plant was recovering before this last batch of snow and rain! Could your plants be getting to wet?