401k loan default questions.

I had a 401k loan outstanding when I was laid off at the end of 2019 (I made all required payments in 2019).  I was unable to pay it off at that time.  The loan went into default in mid 2020.  I thought I still had until I filed my 2020 taxes before it was treated as taxable income(per the 2017 Tax changes).  I repaid the loan in November 2020, but I still received a 1099R with code 1L on it.  Should I be receiving a revised 1099R? or how do I prove to the IRS that I repaid the loan?

Your expectation of the deadline for payment was incorrect.  In addition to the maximum time allowed by law (not your tax day, in any case), the plan generally can set a shorter deadline for default and deemed distribution.  Note that I am oblivious to any effect of the CARES Act. You now have basis in the amount of the balance you paid.  That is some consolation.

Did you repay the loan to the plan or had you rolled money to an IRA and repaid it there?  

I repaid it to the plan.

I'm confused. If you were laid off shouldn't the Code have been 1M since you had a separation from service? 1L indicates the loan is defaulted and not eligible for rollover treatment, 1M would indicate a qualified loan offset due to loss of employment or termination of the plan that is eligible to be rolled over by the extended due date of your tax return for the year of offset under the change you mentioned. 

17 hours ago, Lou S. said:

I'm confused. If you were laid off shouldn't the Code have been 1M since you had a separation from service? 1L indicates the loan is defaulted and not eligible for rollover treatment, 1M would indicate a qualified loan offset due to loss of employment or termination of the plan that is eligible to be rolled over by the extended due date of your tax return for the year of offset under the change you mentioned. 

I agree.  Although I suspect they didn't consider a layoff a termination of employment.

And someone should have said. when you went to repay it: "hey do you realize the loan defaulted and this does not fix that?" (!)