compare-two.txt
This works: <paste>
This doesn't: <paste>

They should behave the same. Diff them properly — not just the
obvious textual differences, but differences in what they actually do:
different data, different timing, different context, different
assumptions about what exists.

List every difference you find, then rank them by how likely each is
to explain the failure.

Tell me which single one to test first.

Also compare the inputs, not just the code. Identical code with a null in one dataset and not the other is the most common version of this.