These are the 19 known galaxies where both Type Ia supernovae and individual Cepheid variable stars have been observed and measured. That’s a very small number, statistically, to draw conclusions about the entire Universe. (S.L. Hoffmann et al. (2016) ApJ, V. 830, №1)

If Cosmology Is In Crisis, Then These Are The 19 Most Important Galaxies In The Universe

Different methods of measuring the expansion rate give different values. This one linchpin is key.

In science, different methods of measuring the same properties should yield the same results.

The expanding Universe, full of galaxies and the complex structure we observe today, arose from a smaller, hotter, denser, more uniform state. It took thousands of scientists working for hundreds of years for us to arrive at this picture, and yet the lack of a consensus on what the expansion rate actually is tells us that either something is dreadfully wrong, we have an unidentified error somewhere, or there’s a new scientific revolution just on the horizon. (C. FAUCHER-GIGUÈRE, A. LIDZ, AND L. HERNQUIST, SCIENCE 319, 5859 (47))

But when it comes to the expanding Universe, two sets of groupsget consistently different outcomes.

A series of different groups seeking to measure the expansion rate of the Universe, along with their color-coded results. Note how there’s a large discrepancy between early-time (top two) and late-time (other) results, with the error bars being much larger on each of the late-time options. (L. VERDE, T. TREU, AND A.G. RIESS (2019), ARXIV:1907.10625)

Signals from the early Universe yield expansion rates of 67 km/s/Mpc, while late-time signals yield systematically larger values.

The best map of the CMB and the best constraints on dark energy and the Hubble parameter from it. We arrive at a Universe that’s 68% dark energy, 27% dark matter, and just 5% normal matter from this and other lines of evidence, with a best-fit expansion rate of 67 km/s/Mpc. (ESA & THE PLANCK COLLABORATION (TOP); P. A. R. ADE ET AL., 2014, A&A (BOTTOM).)

However, every individual measurement is subject to errors and uncertainties inherent to the method used.