It turns out that there are two different subtypes of type 1a supernovas, with one more common in the early universe, and the other more common recently. They are very hard to distinguish in the visible light spectrum, but have clear differences in the UV spectrum. As a result, the rate at which the universe is expanding, if indeed it is expanding, and the amount of dark energy in the universe, are systemically overestimated by a significant amount.
Less dark energy may, however, mean that another cosmology mystery is more profound. This could bring the relative amounts of dark matter and dark energy in the universe closer together, something that is already called the cosmic coincidence problem because there is no obvious theoretical reason for the two dark components of cosmology to be so similar in aggregate amount.