What observational finding directly challenges the assumption of strict isotropy in the universe's evolution?

Answer

Recent findings indicating the expansion rate could be slightly lopsided

If the rate of expansion varies depending on the viewing angle, the universe would be anisotropic, directly challenging the assumption of strict isotropy across all aspects of cosmic evolution.

What observational finding directly challenges the assumption of strict isotropy in the universe's evolution?
universeobservationcosmologydirectionisotropy