In Martin Potts & Associates, Inc. v. Corsair, LLC (2016) 244 CA4th 432 defendant was defaulted and its long time counsel simply said the failure to respond was his fault but did NOT state the reason for not filing a timely response. The trial court set aside the default and plaintiff appealed. The Second Dist. (Div. Two) affirmed and said mandatory relief means mandatory relief and only needs a declaration from the attorney stating that the default was caused by his mistake, inadvertence, surprise, or neglect. The Court held the reasons for the default do NOT matter, even if the reason is inexcusable neglect
Note, that if a default judgment is entered, the time to undo that may not be six months (e.g. CCP 473) but ONLY 60 days from the date of the notice of entry of judgment (See CCP §663a and Garibotti v. HInkle (2015) 243 CA4th 470)