Do you know what could have caused that?
From the information I’ve been able to find: plugins or using its associated filter. (Also, if you’ve had the site for a while, it could have been turned on a long time ago when it was an in-dashboard option, and that setting would have been carried over even though newer versions have it turned off by default).
Otherwise, what are the “risks” to turn it back on 0 again (since I’m on multisite)?
I’m not seeing too many risks, since it’s just changing a 1 to a 0; that being said, I tend to live on the edge more than I probably should when it comes to this sort of stuff, so in your case, I’d suggest making a database backup before doing it (so you have a recovery option). ??