This sounds like classic creative fatigue hitting your retargeting/mid-funnel audiences. Even if top-of-funnel metrics look okay, the people most likely to buy have seen the ad too many times and are tuning it out. Try taking your winning concept and creating 3-4 new variations (different hook, different music, same core message). I use AdsTurbo for this so I don't have to reshoot everything. A fresh look often revives that mid-funnel conversion rate.