In learning general relativity, I am getting confused about which energy conditions (weak, strong, null, dominant) must actually be fulfilled for a spacetime to be considered "valid" in the context of other physics - for example the Alcubierre drive isn't considered valid because of the huge negative energy densities. These negative energy densities violate the WEC and also a bunch of other things so the Alcubierre metric is considered unphysical.
But I also considered Minkowski space with a positive cosmological constant (de Sitter space if I'm not mistaken) where $g_{\mu\nu}=\mathrm{diag}(-c^2,1,1,1)$, or equivalently $g_{\mu\nu}=\mathrm{diag}(c^2,-1,-1,-1)$ in the opposite metric signature. I know that this metric has a null Einstein tensor, so solving the EFEs gives
$$G^{\mu\nu}+\Lambda g^{\mu\nu}=\kappa T^{\mu\nu}=\Lambda g^{\mu\nu}=\Lambda\begin{pmatrix}-\frac{1}{c^2} & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 \\ 0 & 0 & 1 & 0 \\ 0 & 0 & 0 & 1\end{pmatrix}$$
or
$$...=\Lambda\begin{pmatrix}\frac{1}{c^2} & 0 & 0 & 0 \\ 0 & -1 & 0 & 0 \\ 0 & 0 & -1 & 0 \\ 0 & 0 & 0 & -1\end{pmatrix}$$
depending on whether we're using $(-+++)$ or $(+---)$ for the metric signature. It seems like for the former signature the weak energy condition would be violated due to the negative energy density of $T^{00}=-\frac{\Lambda}{\kappa c^2}$ in the first SET, which I doubt because as far as I am aware the two signatures are identical.
I'm confident that the WEC and EFEs and whatnot are all valid, and also that our understanding of the cosmological constant is more or less valid, so what am I missing here? Or does the nonzero cosmological constant cause energy condition violations? We seem to live in a more-or-less flat spacetime with a nonzero cosmological constant, but how is our spacetime allowed in that case if it seems to violate the WEC?
