I had a high end brush, not a Simpson, that shed what I considered more than normal. I notified the vendor and he said to use it for 3 months and if the shedding continued he would replace it. I saved the shed hairs and at the end of 3 months had over 100. He replaced it.

I used the replacement for a year or two and it never shed a hair. Then I lathered a puck I had grated to put in a container. The surface was a bit rough but I didn't think anything of it. Subsequently that brush began to shed like 10 hairs every time I used it. Far more than the one it replaced.

This went on for months and months. No telling how many hairs it lost. It finally stopped shedding and even with as much as it lost is still plenty dense. I'm not sure how many hairs are in an average shaving brush but it is thousands.

If it continues to shed at a steady rate I would contact the vendor, but I wouldn't worry about a relative few hairs.