There is evidence that up to a quarter of transgender genital surgeries result in incontinence.
A systematic literature review  found that 21% of male-to-female patients and 25% of female-to-male patients suffered from incontinence as a result of transgender genital surgery.
One recent study  estimates the number of post-operative transsexuals suffering stress incontinence to be 23%. This study was not a literature review, and almost all of the participants were male-to-female.
 Nassiri, N., Maas, M., Basin, M., Cacciamani, G.E. & Doumanian, L.R. (2020). Urethral complications after gender reassignment surgery: a systematic review. Int J Impot Res. [Link]
 Kuhn, A., Santi, A. & Birkhäuser, M. (2011). Vaginal prolapse, pelvic floor function, and related symptoms 16 years after sex reassignment surgery in transsexuals. Fertil Steril. 95: 2379-82. [Link]