  We find the recently developed strongly constrained and appropriately normed
(SCAN) functional, now widely used in calculations of many materials, is not
able to reliably describe the properties of deep defects and small polarons in
a set of wide-bandgap semiconductors and insulators (ZnO, ZnSe, GaN,
Ga$_2$O$_3$, and NaF). By comparing first-principles calculations using the
SCAN functional against established experimental information and
first-principles calculations using a hybrid functional, we find that the SCAN
functional systematically underestimates the magnitude of the structural
distortions at deep defects and tends to delocalize the charge density of these
defect states.
