The UV map for the Robloxian 2.0 rig is distorted on the upward face of the torso. This is only an issue on the R15 torso of the rig, not the R6 issue. See the images below:
The first image showcases the Robloxian 2.0 rig on an R6 avatar, without any distortion issues on the top face. The second image showcases the Robloxian 2.0 rig on an R15 avatar, which has the top face distorted as you can see.
Expected behavior
Revisions to the UV map to ensure clothing fits as intended for both R6 and the R15 variations would be ideal to resolving this issue.