Optimization of vortex pinning in REBCO coated conductors has been very successful in recent years, but here we report that strong current-limiting effects can still be present in even highly optimized samples. We studied a state-of-the-art MOCVD IBAD-MgO coated conductor, finding it to have a global pinning force Fpmax(77 K, H ∥ c axis) that reached 11 GN m−3. Using low temperature laser scanning microscopy (LTLSM), we found that the local electric field in the flux-flow state was very inhomogeneous and dominated by a high density of a-axis grains, which obstruct current flow on dimensions of several µm. By carefully cutting narrow tracks without such grains in the path, Fpmax rose to 17 GN m−3, a value exceeding all but a very few, carefully made research films. That today’s coated conductors can develop exceptional vortex pinning properties, while still losing a significant fraction of the current density to blocking by growth defects, emphasizes that coated conductor development requires simultaneous attention both to enhancement of vortex pinning and to minimization of current-blocking defects.