CSS View Transitions only working 50% of the time

Hi all, Am definitely new to view transitions so definitely could be making a mistake, but I find that cross document transitions only work 50% of the time. They also don't seem to work reliably at all if you throttle the connection. Can anyone see what I'm doing wrong? https://stackblitz.com/edit/withastro-astro-lwohjq?file=src%2Fpages%2Findex.astro *edit: when the problem occurs the vertical scrollbar seems to also flicker, not sure if that's relevant