LLC Taxed as S-Corp - Family Attribution for Form 5500

Hi, 

I know this has been posted a few times over the years but our actuary is questioning the reasoning. 

We have an LLC that is taxed as an S-corp.  The owner only has one employee, her mother.  Based on several discussions, I thought they would file an EZ.  However, our actuary disagrees and based on 29 CFR §2510.3-3 says that it is should be an SF.  The 2025 Form 5500 filed for the 401(k) plan by a big box TPA filed as SF.  

What say you?  Does it matter that it's an LLC taxed as an S-corp - does it actually have to be an SF corp? 

I used these prior discussions to build my case:

Solo 401(k)Plan - 401(k) Plans - BenefitsLink Message Boards

2% Sharholder of S-corp: attribution included for 5500-EZ - Form 5500 - BenefitsLink Message Boards

thanks!  Hope you are all having a nice long weekend.  

There might be more than one plausible interpretation of the Form 5500 instructions.

It might matter whether the particular limited-liability company is, for Federal income tax purposes, treated as a disregarded entity, a partnership, or an S corporation.

But for a limited-liability company that is not actually a corporation, a classification for Federal income tax purposes might not matter.

Have you considered asking EBSA’s Office of the Chief Accountant for a view about which interpretation EBSA might prefer?

Whatever might be required or permitted Form 5500 reporting:

If the owner’s mother (even if she might be an attributed owner for one or more purposes) is not an actual owner and is an employee within the meaning of and to apply ERISA § 3(2)(A), the retirement plan likely would be ERISA-governed.

If so, and if the plan administrator’s interpretations of the Form 5500 instructions do not point in a clear direction, might the administrator prefer a form used widely for ERISA-governed plans over a form used most often for non-ERISA plans?

This is not advice to anyone.