The cosmic infrared background is the integrated heat of all the dusty star formation that ever happened: dust grains absorbing starlight and re-radiating it in the infrared, summed over every galaxy at every epoch. Its angular fluctuations encode where and when that star formation occurred, and cross-correlating the CIB with galaxy surveys, weak lensing maps, and the X-ray and microwave backgrounds dissects the glow into its source populations (Kashlinsky et al. 2018; Maniyar et al. 2021).
The dissection keeps finding more than the model cooked. ΛCDM halo models fit the broad cross-correlations only with tuned bias factors, redshift distributions, and star-formation efficiencies, and two residuals persist through the tuning: excess CIB power on large angular scales beyond what standard clustering of standard star-formers produces, and a coherence with other backgrounds, notably the X-ray background, stronger than the known shared populations explain (Cooray et al. 2012; Viero et al. 2013). Both residuals point the same direction, toward source populations earlier, more clustered, or more numerous than standard galaxy-formation histories supply, the background-light face of the same early-universe strain JWST sees object by object.
The standing is a budget argument running in parallel with the resolved-source crisis: the unresolved glow and the resolved galaxies are converging on the same conclusion, that star formation and accretion started earlier and stronger than hierarchical assembly allows.