Test in Seedance

A still is only a hypothesis. Run the motion your shot actually needs in Seedance, then change one variable at a time until the visible failure points to the source asset or the motion direction.

Start from a baseline you can diagnose

When the character is the question, keep the location out of it: use a plate that already holds its geometry, depth, materials, and light. A broken plate gives every character failure a second plausible cause.

Diagnose the failing input

One bad clip is a symptom, not a diagnosis. Compare its first failure with the source stills, then read the controlled result.

Visible pattern	Working diagnosis
Defect exists in the source or stays tied to the same feature when direction changes	Source asset
Source is clean and the defect changes when only the suspect motion clause changes	Motion direction
Controls conflict or the failure follows neither variable	Inconclusive — narrow the test

This diagnosis applies to the tested asset and direction. It is not a universal claim about a model, and one rerun does not guarantee the next result.