The Cosmic Microwave Background polarization power spectrum exhibits an unexpected enhancement or "bump" in power at intermediate angular scales that is not well-explained by Lambda-CDM's predictions for how polarization should scale with temperature anisotropies and Thomson scattering during reionization. The polarization pattern depends on the optical depth to reionization (how much ionized material lies between us and the CMB surface), and standard models predict a specific relationship between polarization power at different scales, but observations show a localized excess in polarization power at certain multipole ranges that suggests either the reionization history was more complex than simple models assume, or additional sources of polarization exist beyond Thomson scattering from free electrons (Planck Collaboration 2018; Hazumi 2020). Lambda-CDM struggles because introducing sufficient reionization optical depth to explain the bump creates tension with other constraints on reionization timing from observations of the 21-centimeter line and from early galaxy surveys, while invoking exotic polarization sources would require new physics beyond standard electromagnetism.