Anybody have experience with LT38 notice from the IRS

I received this notice saying I owe $5K from the 2020 tax year. The reason stated is that they relaxed the notifications during the pandemic. However, I have filed and paid as directed for the last 15 years with the same CPA.

Has anybody had to deal with this? How should I go about fighting it? I will be in contact with my CPA, just wanted to see if this was something happening on a wider scale.