Eyebrow Hair Loss After IPL

If the hair loss happened after only 1 IPL treatment, you should expect to see re-growth, since it typically takes 6 or more treatments to get permanent hair reduction.
I also think that consultation with a board-certified dermatologist familiar with IPL or laser hair removal would be very helpful.
Best regards.

Certainly, this can happen, the light from the IPL does reach the hair follicle and can send the hair into the resting phase, telogen, in which it would fall out a few weeks later. It of course can cause, if too much fluence was given cause destruction of the matrix of the follicle, in which case the hair will not grow back.
Other entities which might have been coincidental might have occurred. For instande you might havedeveloped alopecia areata which effects only certain areas of the eyebrow, Certainly thyroid disease can cause the same problem.
I would return to the phsician who runs the cosmetic spa, hopefully a dermatologist, the these days who knows. Your dermatologsits can make the proper diagnosis and recommend atreatment plans.