The cover and the filling may have different care requirements. A washable-looking outer fabric does not establish that the complete pillow tolerates machine treatment.
Understanding this situation
Some fillings need a specific washing and subsequent drying method, while a damaged seam can release material into the machine. The appliance also needs a programme and capacity suitable for the complete item.
A useful next step
Read the pillow's own instructions before loading it and check for weakened seams. If filling escapes during a cycle, stop treating it as ordinary lint and seek model-specific cleaning advice once the appliance is safe. Do not continue washing unrelated loads through the debris.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.