Cellranger multi with single sample: reads not assigned to sample

Question

[Igor]

I have a 10x scRNA-seq + V(D)J + Antibody Capture experiment (see the image). I've used CellRanger to process the data using the multi command (a recommended way as per 10x docs). The output has separate sections for "Sample" and "Library". The number of reads under the "Sample" is smaller than the one in the "Library". Does anyone know how are those different for a single-sample library? Why would some reads not be assigned to the only sample in the library?