@kelsmom can comment…but I believe your son, for loan repayment purposes, has not been a student since 2018. To have loans not enter the deferral period, the student needs to be enrolled at least half time in college.
@kelsmom can tell you if this enrollment needs to be as a matriculated student.
I suggested you start with the college because this is a Perkins Loan. So…start there. But as @Kelsmom note, your loan servicer is giving you an opportunity to deal with this…and that is very worth your consideration.
What is the total amount owed? Is there any chance you can just pay this loan off?
ETA…good luck to your son this term! It sounds like he is re-entering college slowly and carefully. I’ve often said…college isn’t a race. It’s a journey. And college will always be there in the future.