I use your v3/questions/ API to get a list of all the questions in my surveys. I've noticed that for matrix questions the data for one or more rows is sometimes missing. Anecdotally it most often seems to happen with the 1st and 3rd row.
This problem occurs both for matrix question where the rows are manually created and matrix questions where we pipe answers. It happens with all types of matrix questions. For matrix questions with piped answers, I've found that changing 'Selected Answers Only' to 'All options' and back fixes the issue somewhat reliably. I haven't found such a workaround for matrix questions where I've manually created and named the rows. Deleting the question and recreating it is one option, but today I had a question that still didn't come through properly, even after recreating it from scratch.
I will try to reproduce in a small survey the problem and share a link here.