The AP1000, was supposed to address construction problems by being able to ship in large parts already constructed. But that failed so miserably that SMRs-long ignored because they weren't thought to be economically efficient-became the last ditch effort to build nuclear. And the AP1000 failed because of all the on-site mismanagement of things as simple as concrete pours.
SMRs are unproven in at least two regards: 1) ability to manufacture in a factory economically, and 2) ability to construct all the on-site infrastructure for the SMR to generate the electricity.