A rug's backing can be as important as its upper fabric. Only machine-wash it where the item and appliance instructions permit the complete construction.
Understanding this situation
Deteriorated backing may shed pieces, and a wet rug can behave as a heavy compact load. The fact that it folds into the drum does not establish a suitable programme or safe capacity.
A useful next step
Check for brittle, cracking or separating material before washing. Use the specified care method and avoid forcing an unsuitable item into the machine. If fragments appear during a wash, stop further laundry use until the permitted cleaning and any fault assessment are understood.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.