Two possibilities:

1. The W-2 was prepared incorrectly and there should not be an amount in box 1. Have the client contact the issuer.

2. The W-2 is correct. They received a code "Code J—Nontaxable sick pay. Show any sick pay that was paid by a third party and was not includible in income (and not shown in boxes 1, 3, and 5) because the employee contributed to the sick pay plan. Do not include nontaxable disability payments made directly by a state." and it was supplemented with taxable pay, e.g. We make you whole. The company matches any third part disability because (they are nice) (the client got covid) ....  Have the client contact the issuer.Have the client contact the issuer.