Evidence for a sign change of the ISW effect in the very recent Universe? Hot voids and cold overdensities at z   <  0.03

We find a significant cosmic microwave background (CMB) temperature excess in the direction of local underdensities within z < 0.03. By contrast, fewer than 0.2% of simulated CMB maps show a similarly significant temperature excess in nearby voids. Combined with earlier findings showing a > 5 σ cooling of CMB photons in galactic filaments in the same redshift range, we now may have possible evidence for a negative integrated Sachs-Wolfe (ISW) effect in the very recent Universe. In addition to having the opposite sign, the observed amplitude is an order of magnitude larger than the predicted Rees-Sciama and ISW effects, pointing to an unknown physical process, possibly related with a non-standard model of dark energy. We discuss the results in light of the latest Data Release 2 results of the Dark Energy Spectroscopic Instrument (DESI) showing hints of dynamical dark energy. Removing the quadrupole, we find the CMB temperatures measured in nearby voids to a large degree uncorrelated with the temperature measured around nearby galaxies, and the observed mean difference between these temperatures is almost 6.5 σ larger than what is found in simulations.