Can releasing of internal muscle fibers between the breast cause uniboob?

Anything can do anything in surgery. However, the usual cause for the "uniboob" is choosing implants that are too large and wide for the base of your breasts.

Dear Genius233157,
symmastia is a rare breast condition that occurs when soft web-like breast tissue pulls breast implants towards each other, until the breasts meet uncomfortably at the center of the chest near the sternum (the body’s midline point). Given this abnormal union, symmastia is known by many other names, including breadloafing, kissing breast implants, and the uniboob.Unfortunately, this condition causes the surrounding skin and pectoral muscles to literally lift off the breast bone as the implants are pulled together. This consequently causes pain and discomfort, as well as obvious distortion of the breasts, which can only be disguised with clothing that does not show cleavage.
Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery

Synmastia is extremely rare even if the muscle fibers are released completely. I have never seen a case in 35 years