Fergus - I've already uploaded a sample file to the Frame space. I would say though that this behaviour is only really apparent when you have a sequence of clips in a timeline not a single piece of media which is why I suspect these issues aren't being caught. It tends to occur more when you have mixed formats in a project as well so that (as previously reported by us) playback tends to get worse over the life of an edit. See also the disappearing waveforms bug in 22.4 onwards which won't show up on a simple test.