If you were current on your loan payments at the time of separation from service in 2018, the plan should have satisfied the loan with an offset distribution, not a deemed distribution, if you chose, or were not permitted, to continue to have the loan and make payments. An offset distribution would have been reported with code M being included in box 7 of the Form 1099-R reporting this distribution, along with code 1 if you were under age 59½. Code L (along with code 1 if under age 59½) would indicate a deemed distribution that is not eligible for rollover. If not rolled over, the distribution is subject to ordinary income tax and, if you were under age 59½, to a 10% early-distribution penalty; there would be no avoiding these.
For rolling over an offset distribution, the SECURE Act extended the deadline to the due date of the tax return for the year of the distribution, including extensions, rather than the usual 60 days for an eligible rollover distribution such as an offset distribution, but it's too late for that now and you would have had to have come up with the money from some other source to be able to complete the rollover.
