In recurrence of bottoming out, is it because of the sutures coming undone or the capsule stretching out?

If the implant has dropped again it is likely the capsule repair has failed. If the left side is ok it is likely to stay that way.

When a breast implant migrates below the original placement location with the bottom of the implant just above the infra-mammary crease, we call this “bottoming out.” There are several causes of this downward migration of the breast implant. Usually, some attempt had been made to lower the crease to accommodate a breast implant whose base diameter is larger than would otherwise fit in the natural breast. In doing so, the anatomic attachment of the skin of the breast to the chest wall can be obliterated. There is then nothing to hold the implant up. With the weight of the implant, and constant gravity, maybe lack of support by lack of wearing a bra continuously, the implant can settle downward. One of the earliest symptoms, I see in patients seeking revision, has been the feeling that the breast has to be constantly adjusted or just feels heavy. We look for the incision line, which was previously placed at the crease, to have migrated upward onto the breast. When we see this early on in the postoperative phase, it will never get better with time and will require a secondary repair. While some plastic surgeons may rely on suturing techniques only, I have found that unless we un-weight the implant by making it smaller or strengthen the tissues below by making them less stretchy, that the same implant, with  only sutures placed on the bottom of the pocket, will, over time, recur it's bottomed out position. I have used part of the capsule as well as the lining of the deep muscles and tissues over the ribs in the capsule beneath the breast implants to rotate upward to hold the breast implant in a higher position and therefore obliterating the extra space that has been created between the correct infra-mammary crease and the one created by the downward displacement of the implant. I call this a three flap technique, as the skin, the capsule and fascia (lining of muscles), as well as a dermal flap all contribute to creating a hammock like support of the lower portion of the pocket. When these tissues are insufficient to hold the implant up, or a previous attempt has been made with sutures, I will oftentimes rely on the addition of another type of tissue called an acellular dermal matrix of which my preference is Strattice. This Strattice, or pigskin, does not stretch and can be sewn in to the bottom of the new location of the crease to support it just like a hammock would. Although this is costly, I consider this an insurance policy against having to redo this again. I would recommend that you try and find a plastic surgeon with experience in revisionary cosmetic breast surgery. Good luck.