It is very difficult for Vanessa to answer all recipe book queries by email I am afraid, she just has so much work on and not enough time. However her advice would always be the following.
Before you start baking any of the recipes in the books, please do read and understand the whole first section of the book, before the recipes start, as this contains all the information you need to then be able to bake the recipes successfully.
There are many variables that may be impacting your baking. It could be that your sourdough starter needs refreshing according to the Schedule for that particular recipe, as refreshment generally gives a better result.
For every recipe, you need to use the same (or very similar) flour, please check which flour has been recommended.
Also, please make sure that your timings and temperatures match the recipe as all of the recipes in the book have been triple tested to ensure the best results are achieved.
If you are still struggling you are so welcome to join Vanessa at an Open Q&A live Zoom session on Thursdays at 4pm (GMT – London time) and ask your question there. Here are the details of our live sessions with instructions to request to join.