Let $$f_\pm(x):=e^x(1\pm c\sin x)$$ for some $c\in(0,1/2]$ and all real $x$.
Then $f_+$ and $f_-$ are increasing differentiable convex functions that agree exactly on the countable set $\pi\mathbb Z$.
Let $$f_\pm(x):=e^x(1\pm c\sin x)$$ for some $c\in(0,1/2]$ and all real $x$.
Then $f_+$ and $f_-$ are increasing differentiable convex functions that agree exactly on the countable set $\pi\mathbb Z$.