Unfortunately, MRIs are unhelpful for interpreting ADRs (artificial disc replacements) due to the large metal mass. The way to interpret ADR dysfunction is with flexion-extension X-rays and a CT scan. I would assume that if the other non-operated levels look “normal” that your problem is with the ADR.
Flexion-extension X-rays are a key piece of information. Does the disc move appropriately and are the endplates intact or had the disc eroded into the endplates or migrated? Most likely, a revision to a fusion will help but more information is needed.