Does Notice CP80 change my filing deadline?

I got a Notice CP80 indicating I have a balance with the IRS on my 2017 taxes. For complicated reasons, I have not yet filed my 2017 taxes. Ultimately I'm owed a refund. The notice says if I don't file, "I may lose this credit," but does not specify any deadline about when that might happen.

 

I understand the normal time limit for claiming my refund is three years from the original tax filing deadline (see https://www.irs.gov/individuals/dont-lose-your-refund-by-not-filing). For my 2017 taxes, that would be April 15, 2021. However, the IRS language says this applies "in most cases". The timing of this notice makes me nervous that perhaps I might forfeit my refund if I don't file today, by the 2019 filing deadline. After multiple attempts, I'm unable to get through to the IRS to clarify this.

 

Unfortunately, there are still several issues outstanding so I'm not able to file a (correct) return today. Is there *any chance* that I might be forfeiting my refund by not filing today?