to zzzzz (Patreon)

To verify the issue you said, I rendered the model from the front. No problems were found there.

A possible cause is lens distortion: using a lens wider than 35 mm will cause distortion on the periphery of the image. The lens I use is 36 mm; setting it to 50 mm would eliminate the distortion. However, setting it to 50 mm has both advantages and disadvantages when used indoors, as the subject feels further away from the camera and obstacles in the foreground (e.g. a man) reduce the area of the subject in the image.

Lens Distortion: What Every Photographer Should Know (clickitupanotch.com)