Dependencies not working when I move start date back

I’ve created planning for a webinar with dependencies. I changed the start date to a future date as I was planning to start it later in the month.

That worked great and all the timelines moved accordingly based on the duration and the dependencies.

However when I moved the start date back to it’s original date, none of the timelines changed, they remained as they were when I updated it to a later date. So I tried changing the start date again to a future date and all the timelines changed, but when I put the start date back to the original date none of the timelines changed and they remained the same.

Not sure what is going on, it seems that if I move the start date to a future date the timelines change according to dependencies and duration but if I move the start date back, then nothing happens and I am stuck with the timelines that altered when I put a future date in.

Any help would be great, I’ve searched and I just can’t seem to find the answer anywhere. I have previously used SmartSheets and you can change the start date backwards and forwards for a project and the timelines adjust accordingly.

I’ve attached a screen grab - if I set the start date back to a date in October all the other November dates remain. However if I set the start date to a future date in December then all the dependent dates change accordingly.