I am in the same situation. I received a check in early April before filing my taxes for 2018. The letter that came with it said 'you should report the pre-tax amount of your excess deferrals on line 7 of your individual tax return (form 1040) for 2018, and you should report the alllocable loss as a bracketed amount on the "other income" line of your form 1040 for 2019.' I do not have to amend my 2018 return because I dealt with it when I filed in mid April.
