So I found the solution to this problem and it’s something extremely odd: I replaced the call to the PhP-defined function unhost() that was doing the unhosting with the effective actions (write on a socket connected to Twitch’s IRC server and type the /unhost command; I litterally unfolder the sequence of function calls to replace the line with an instruction). The functions host() and unhost() were doing exactly the same thing, except the messages being sent are host and unhost, and for some unknown reason the second one was not working.
If anyone more knowledgeable in Twitch API and/or PhP has any idea of why that is, I’d very much appreciate the enlightenment 