While he's the most recent one, it's been a systemic problem that's largely been from congressional budget cuts.

2014 The War on the IRS https://taxpolicycenter.org/taxvox/war-irs

2015 Poor IRS Service Reflects Congress’s Deep Funding Cuts https://www.cbpp.org/research/federal-tax/poor-irs-service-r...

2018 How the IRS Was Gutted https://www.propublica.org/article/how-the-irs-was-gutted

2020 Congressional Budget Office Confirms That IRS Budget Cuts Lose Money and Benefit the Rich https://itep.org/congressional-budget-office-confirms-that-i...