What are the consequences of a sentence that does not require a mandatory fee to be imposed at sentencing?

^3. It is of no consequence that the People failed to object to the waiver of these fees at sentencing, or that the imposition of the waived fees will increase the funds defendant is required to pay. The failure to impose a mandatory fee renders a sentence illegal, and must be corrected on appeal. (People v. Woods (2010) 191 Cal.App.4th 269, 272-273.) An unauthorized sentence "is subject to being set aside judicially and is no bar to the imposition of a proper judgment thereafter, even though it is more severe than the original unauthorized pronouncement." (People v. Serrato (1973) 9 Cal.3d 753, 764, fn. omitted [disapproved on other grounds].)