Thank you for your reply Daniel.
Regarding the search issue, I do not think it is server-related as everything works perfectly with Pinboard 🙁
The problem is that when you are on a page other than the home page and you run a search, the “?s=xxx” part is appended to the URL of this page instead of being appended to the home page URL, so when you are in a category, it returns results in this category only, and when you are on a single post page, it returns a 404 error…
Here is my site address in case you want to try : http://www.lecoinduson.fr
Thanks for your help!