Which invariant reactions are congruent?
You are correct, none of the reactions are congruent reactions.

Per IUPAC GoldBook:


  Congruent Transition: A transition in which the two-phase equilibrium of melting, vaporization or allotropism of a compound involves phases of the same composition.


The key term here is "phases of the same composition." Since all of the reactions have two phases transforming into one phase (or vise-versa) the reaction is not congruent.

See the phase diagram for silicon and titanium. Congruent melting occurs for $\ce{Ti5Si3}$ and $\ce{TiSi2}$ where you observe a $\ce{\color{red}{comp A (s)} -&gt; \color{red}{comp A (l)}}$ transition, whereas at the eutectics you have $\ce{\color{blue}{comp B (s)} + \color{green}{comp C (s)} -&gt; \color{red}{comp A (l)}} $ transition where $\mathrm{B \ne C \ne A \ne B}$. Thus the eutectics are not congruent transitions.