Unless you are really observant, it is easy to miss scratches on the surface of the wood after it has been sanded. But once the finish or oil has been applied, these scratches become painfully visible for everyone to see.
The problem may be due to a poor abrasive with pieces of grit that become easily detached. Even if you vacuum clean the floor after each sanding step, you do not always remove loose pieces of grit. Some of them remain in cracks in the floor. The vibrations of the machine as it passes over can make them bounce up again and they could fasten under the back wheels or in the abrasive itself.
The sharp pieces of grit can fall off the surface of a poor quality abrasive. Bona Abrasives, on the other hand, are made with high quality adhesives to hold the pieces of grit in position and minimize the risk of scratching.
Practical tip: after every change of grit number, vacuum clean the floor because any coarse grit lying around can damage the finer abrasive that follows