Coupon Already Used

Hi

I created a 1000 coupons, however, when we tried the coupons out ourselves and had a selected few customers used the coupon something like this pop out ONLY at checkout when choose to make payment.

“Coupon zjxr-n4pj-xwj7 was used in another transaction during this checkout, and coupon usage limit is reached. Please remove the coupon and try again.”

However when I went back inside backend the code or the codes by our customers were not used yet. it was still 0/1

However, I did try to delete 1 of the code and create the exactly same one it works. but not the one created by the plugin.

My current versions:
Woocommerce 3.9.3
Wordpress 5.3.2