Fluid filled lump on incision site 6 months after revision - what might this be? (photo)

I'm 20F and I had my breast augmentation in March 2022. The left breast was a lot smaller than the right breast so a much bigger implant was usee to make equal. I had surgery again on my left breast in July and everything was healing fine. Then randomly in October I noticed this lump filled with fluid on the incision site. Turns out it was not an infection but no doctor i've seen knows what it is.