I now think that my actions had no effect but the preview system is taking 30-45 minutes to start, and I was assuming that whatever I was doing was having an effect, then the next day I started with that and it didn't work, because the only thing that was working was waiting for an incredibly long time. I have created a Feedback item at FB8988812.

Thank you for this. The delete all command does work, but I have to run it every time I resume the preview or I run into the same problem, which feels a little wrong.