What can cause back spasms on the lower left back just above the ribs while eating?

Varies. There are multiple potential causes. It can me musculoskeletal, such as in a paraspinal strain; it can be from a pinched nerve in the back; it can be from things in that area such as a kidney or pancreas problem. I would not hesitate to be seen and evaluated for an accurate diagnosis.
Spasms. I wonder if you may have esophageal spasms that are felt in your back. The esophageal (foodpipe) spasms may refer to the back and that may be the reason why you feel them there. The pancreas pain may also refer to the back but it is usually severe and normally happens after meals, whereas esophageal spasms are usually during the meal.