I'm a fellow user--not a tax expert. Perhaps the second letter was generated if they hadn't processed everything you sent after the first letter; i.e., a case of the left hand not knowing what the right hand is doing.
Is there an IRS phone number on the 178C letter? If it was me, I'd probably phone the IRS, explain what was previously sent and the subsequent duplicate letter, and ask them outright what they want me to do in this instance. Maybe they can explain why the second letter was sent, or whether it was redundant.
Or if there's not a contact number on the letters, the main IRS phone number is 800-829-1040 (7AM-7 PM local time) Monday-Friday
OR since you purchased MAX, that company that offers the audit defense product should be able to help you with an IRS Letter. You can phone them and see. It shouldn't hurt to ask. Contact info is in the right column of the table displayed in this article:
TurboTax Audit Support Center
https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-audit/turbotax-audit-support/L6AcMoN...
TurboTax also has a free Audit Support Center that will help folks with an IRS Letter. Contact info is in the table in that same article mentioned above.
