If your husband started collecting his Social Security along with becoming eligible for Medicare in February, this amount could have put you over the income limit for your advance payments.
He could still keep his Marketplace policy after becoming eligible for Medicare, but would not be eligible for a tax credit for those months.
Here's more info:
https://www.healthcare.gov/medicare/changing-from-marketplace-to-medicare/
Edited 3/17/18 7:09 pm
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