It sounds exceedingly rare based on some case studies that I’ve read.
The interesting part is that it sounds like it doesn’t have a huge effect on blood flow at rest, so in general we measure leg blood flow with something called Ankle Brachial Index, which essentially is a ratio of leg to arm blood pressure. In athletes with endofibrosis they tend to have normal ABI at rest but it will be reduced after exercise. Essentially means that the evaluating physician needs to be looking for endofibrosis specifically to test for it.