A loan from a 401(k) account does not generate a Form 1099-R. You only would have received the 1099-R if you had a distribution from the 1099-R.
What code is in box 7 of the 1099-R? Is there an amount entered in box 2a?
What is the code on the 1099-R box 7? Is the IRA/SEP/SIMPLE box checked?
You cannot normally "borrow" money from a 401(k) unless you take a loan from the plan and a 401(k) loan is not reported and cannot be rolled back but it can be paid back and that does not produce a 1099-R. Most plans do not permit taking distributions and then rolling them back.