Correcting your plan’s late deposit of salary deferrals by depositing them and making a contribution to make up for lost earnings in your 401(k) plan isn’t enough.
Why? Well, Form 5500 requires you to truthfully answer whether you have late deferrals. If you answer yes (well you have to under penalties of perjury), it will alert the Department of Labor (DOL) as to your issue. The DOL will check their files and see if you filed a Voluntary Fiduciary Compliance Program, application with them. If you didn’t, they will contact you and give the suggestion you should, which would also include Form 5330.
Many plan sponsors don’t do that because of the cost and wait to hear from the DOL. Speaking from experience, I’d rather nip problems in the bud and complete the issue ahead of time.