Are these failed grafts popping out 3 to 4 months post FUE? (photos)

Thank you for the photos.  3-4 months is late to shed, but its's also unlikely that your follicles aren't integrated into the scalp by now.  Follow up with your doctor who can examine you.

If they look a like a dried up tissue it may be a lost graft.  It can happen after surgery .  If you are concerned it is best to discuss with your doctor.

At between 3-4 months most of the shedding should have been completed, but clearly in your case, there appears to still be some grafts that are shedding late.