"Update citations and bibliography" showed same reference in the main text

Today after I clicked the “Update citations and bibliography” button in Word to make the changes visible in the reference list, same reference appeared in my main text, but not references list. Reference in main text were increase sequentially after I clicked the “Update citations and bibliography” button.

For example, clicked “Update citations and bibliography” button three times, three “(Imai et al. 1997)” appeared in main text as below:

CX3CR1 is a 7-transmembrane domain G-protein-coupled receptor of CX3CL1 (Imai et al. 1997)(Imai et al., 1997)(Imai et al., 1997).

Any help or advice would be very much appreciated.