Correcting Plan Covering Puerto Rico Employees Without Dual Qualification

[401 Chaos]

Does anyone have experience or recommendations for resources discussing a regular US 401(k) plan that has covered Puerto Rico employees without regard to the dual qualification requirements and/or specific rules / limits, etc. applicable to Puerto Rico employees. (Basically employer treated adding Puerto Rico employees just like adding employees of a regular state for 401(k) purposes and did not realize the issues with that until a former PR employee tried to roll over his distribution.)

I feel like I have seen this issue discussed on boards here or possibly in some journal articles before but cannot seem to find much information. I'm thinking this must not be an completely unknown issue but not sure how / if they could go about correcting with the Hacienda and/or IRS. Thanks