Istanbul code coverage html report ambiguity

I'm writing some Mocha tests to test some React code, and I'm using Istanbul to check my code coverage. Most of the time when I hit a line of code, I see a green highlighted number to the left of the code with the number of times I hit it and the code itself is not highlighted like so:

However, in another file, I'm certain that I'm hitting some lines of code, and I'm getting the green highlighted number on the left, but the code itself is highlighted in red like so:

Does anyone know why in the second example the code is covered but is highlighted in red?