B2 visa revoked

Hi,

My parents visited us last year and they were supposed to leave by September 2019. But since I was sick , they had to extend and I applied the extension for both of them and we got the receipt for both of them . Unfortunately there was an emergency for my sister and so they had to return to India immediately. Fortunately my dad got the fingerprint appointment just 2 days before they left but my mom didn’t get the appointment letter . Later we got the letter a week later that her appointment is same as my dad’s . But by the time they left to India . So they left by October 2019 .

Now yesterday I got an email that my mom’s US visa was revoked and they will ask my mom to physically come to chennai ofc when they reopen to physically cancel the current visa in passport . Is thfere anyway to know why my mom’s visa is revoked ? Any way that it can be reinstated? Please help .

Thank you all in advance .