Stubben and Indian leather saddle
The pommel is too low creating pressure on the withers. Above is a horse showing white hairs on the withers from a saddle being too close.
Channel through the back of the saddle too narrow - only 2 1/2 fingers wide, which is sitting each side of the spine and pinching. The space needs to be around 4 fingers.
Saddle channel too narrow sitting close to the spine. This will restrict the horse from bending and cause hollowing in the back.