It looks like your pachysandra has symptoms of Volutella blight. This is a common fungal disease on pachysandra that attacks both the leaves and stems. It is more often on plants growing in sunny locations. It is most severe in overgrown plantings and is also often associated with scale (insect) infestations.

You can try to manage this disease using cultural practices that minimize leaf wetness and increase air circulation around the plants. Remove symptomatic leaves/stems. If there are large areas showing symptoms, you can put a mower on its highest setting and mow over the pachysandra with a bag attached to catch debris or rake up the symptomatic debris. Avoid overhead irrigation and thin new growth to increase air circulation, which will promote faster leaf drying. Anything that keeps the leaves more dry than wet is what you are after. The longer leaves stay wet, the more likely that diseases can get out of hand. Fungicides suppress the disease but do not cure it.

Refer to our webpage for more information.
https://extension.umd.edu/hgic/topics/volutella-dieback-pachysandra-groundcover

If the disease continues to persist and becomes too difficult to manage, you might consider planting some alternatives to pachysandra. Several options are included in this article.
https://marylandgrows.umd.edu/2019/05/06/my-pachysandra-is-dying-what-can-i-plant-in-its-place/

Christa