On 2.99.8 I still have this issue - if I add a format file to an existing book, it doesn't appear on the running server. It looks like it can be overcome by refreshing the site. I can do that via a Library Switch, but what if I only have one library. Or I can do it by restarting the browser, assuming I know how to do that.**
Maybe a site refresh 'button' is needed.
- Why are so many browser functions that were once easy to do, now a PITA. FX to restart Firefox 53.03 with same tabs etc, it's 'open a browser console window and type "restart";.
How many regular people know how to open a 'browser console' let alone where to type the 'restart'. There was a time when the Firefox File menu had a Restart option.
Chrome's not much better, but at least its method is bookmarkable
BR