  Within the Friedmann-Lema\^itre-Robertson-Walker (FLRW) framework, the Hubble
constant $H_0$ is an integration constant. Thus, consistency of the model
demands observational constancy of $H_0$. We demonstrate redshift evolution of
best fit $\Lambda$CDM parameters $(H_0, \Omega_{m})$ in Pantheon+ supernove
(SNe). Redshift evolution of best fit cosmological parameters is a prerequisite
to finding a statistically significant evolution as well as identifying
alternative models that are competitive with $\Lambda$CDM in a Bayesian model
comparison. To assess statistical significance, we employ three different
methods: i) Bayesian model comparison, ii) mock simulations and iii) profile
distributions. The first shows a marginal preference for the vanilla
$\Lambda$CDM model over an ad hoc model with 3 additional parameters and an
unphysical jump in cosmological parameters at $z=1$. From mock simulations, we
estimate the statistical significance of redshift evolution of best fit
parameters and negative dark energy density ($\Omega_m > 1$) to be in the $1-2
\sigma$ range, depending on the criteria employed. Importantly, in direct
comparison to the same analysis with the earlier Pantheon sample we find that
statistical significance of redshift evolution of best fit parameters has
increased, as expected for a physical effect. Our profile distribution analysis
demonstrates a shift in $(H_0, \Omega_m)$ in excess of $95\%$ confidence level
for SNe with redshifts $z > 1$ and also shows that a degeneracy in MCMC
posteriors is not equivalent to a curve of constant $\chi^2$. Our findings can
be interpreted as a statistical fluctuation or unexplored systematics in
Pantheon+ or $\Lambda$CDM model breakdown. The first two possibilities are
disfavoured by similar trends in independent probes.
