Cording

Cording refers to the development of palpable cords (tight bands) usually in the axillary region when it is called axillary web syndrome (AWS). Reported rates vary widely. There is little known when it occurs, or why it occurs, or how long it lasts.
Tight cords under the axilla limits range of motion, and sometimes aggressive stretches are used to improve shoulder mobility.
Not only is there little known about the origin (dilated thrombosed lymphatics, or thrombosed superficial veins, or both), risk factors are guesses, and it is unclear how to treat it.  Physical therapy (stretches), non steroidal anti-inflammatories, heat packs, lymphatic massage has been mentioned.
Some forums say there is little one can do to speed up the process.

In a literature review of 8 studies symptoms lasted between 1 week to 2 years, most resolved within 3 months. The prevalence can be high depending on the studies, there is no consensus on definition, treatment, or standardized screening.

References:

Piper M, Guajardo I, Denkler K, Sbitany H. Axillary web syndrome. Current understanding and new directions for treatment. Ann. Plastic Surg 2016; 76:S227-S231.

Moskovitz AH, Anderson BO, Yeung RS, et al. Axillary web syndrome after axillary dissection. Am J Surg. 2001;181:434–439.

O'Toole J, Miller CL, Specht M, Skolyny M, Jammallo L, Horick N, Elliott K, MNiemierko A, Taghian A. Cording following treatment for breast cancer. Breast Cancer Res Treat 2013; 140:105-111.

Even less is known about truncal cording "What is Cording?" National Lymphedema Network

This may be a case of underreporting, especially if the truncal cording does not limit daily activities or causes pain.

However I was not happy to have discovered this across my abdomen during the 5th week postop (see photo of left side during a lunge stretch).  Best guess: possibly due to overdoing the GHD sit-ups (3 sets of 10). To be continued ....