You have SKUs A, B, and C all on the same variation listing in Listing Mirror. However, on the Walmart marketplace, all 3 SKUs are not being grouped together on the same marketplace listing.
Enable the field Primary Variant for one of the SKUs of the variation listing. It does not matter which one. This field can be found on the edit listings page, under "Child Listing Fields."
This should force Walmart to regroup the SKUs on the Walmart marketplace based on how they are setup in Listing Mirror. Give Walmart about 24 hours to update this. After that time, if it does not work, please contact use at Support and we'll lend a hand!