The size of purpose band and MW will be a lot different in western blot?

1. It may be that the concentration of the gel does not correspond to the concentration of the protein of interest, such as a high concentration of gel for larger proteins.  

2. There is protein degradation, and the main band is likely to appear lower than the original position, but also there will be some other stray bands, the most important feature is that all the bands are lower than normal, and the bands are blurred and unclear.  

3. You can conduct experiments to rule out the possibility that the 25 kDa is a stray band, it may be that your sample does not express a protein, and the protein is a non-specific band caused by the antibody.