I’m sorry, I was mistaken.
I found the issue, but I may need FTP details to be able to resolve this. I tried to login via FTP with the given details, but it does not seem to work unfortunately. Can you please check that?
The issue is that the character “İ” lowercases to “i̇” (ı + a special dot character) and that is not the same as “i”. So searching “i̇yi” will give results, but searching “iyi” will not – because those are not the same letters.
I can probably code an exception there to index both versions of the word where this special character is found.