L2-HGA - Newton SBT

This happens to my dog when he has exercise and we would like your help. Vets haven’t seen this behavior before and are very confused, he has had Xrays done which have come back clear. We are looking to send him to a specialist has this is very upsetting for him and us. Update: Our Staffie is currently being tested for L2 HGA. Update: confirmation he as L2 HGA Here is a fit showing a wobb;y walk 5/10.