The search gets indexed once every hour and for a few seconds it doesn't work correctly, I suspect you may have tried at precisely that moment, just a coincidence. Also, an unexpected surge in number of visitors may trigger the Cloudflare protection, but in those cases the system warns you that "you cannot use the search at this moment". This lasts only for a few minutes, then all goes back to normal.
About your second question and the search: our Rules
require that all titles in the same series (or standalone novels by the same author) should be posted in the same release. So if you use the Quick search, you will need to open all posts with a number of books in the subject to see all the titles inside.
Therefore, it is always easier and quicker to use the Advanced search to find a title inside a post.
1. Click the button to open the Search: https://images.mobilism.org/?di=V2K9
2. Enter the name of the author (no hyphens or dashes) along with the title you are looking for as keywords (i.e. Mikhail Bulgakov Master Margarita)
3. Select 'eBooks Releases' in the "Search in forums" drop-down menu (or select the category, if you know it)
4. Tick the option 'Post subjects and message text' in "Search within". Like this:
Mobilism 2.0: https://images.mobilism.org/?di=IK38XNTC
Classic skin: https://images.mobilism.org/?di=DCHEANAQ