Thanks, Simon. I'll take another look but I don't think height is set initially, but there may be a workaround.
We actually do use randomisation and question banks, but unless I'm missing something all the questions are still displayed once the result is calculated (and displayed in a separate article below the questions article).
We only display the pass or fail icon, but it can still be enough to screenshot.
I was also having issues with where to place any custom jquery. I was calling it from theme.js (from a customised vanilla theme) as a test and could get a successful console message on the assessment page load, but it wouldn't seem to work once the assessment was started (after clicking a trickle button to show the first question).
I'll figure it out eventually but just wasn't sure if others had looked into this already.