Practically none of the mods I want to install are working and I even had to re-install the entire board then restore the theme from an older backup when I tried to install one of the mods (I forgot which one, but the entire board ended up into white screens of death). In some other cases, some mods don't even do anything at all, even on the default them. Example: Stop Forum Spam, which changes absolutely nothing at all.
If you check SMF website, you will notice that there is only 1 single post mentionning HHVM out of their 3 million messages and it's in Spanish. I wonder if the SMF team is even aware that it exists at all.
I know some of you prefer HHVM because it's much faster than PHP, but it's severely slowing down site progress and now I'm pretty much forced to halt mod install and editing until we did the switch. I would rather use something slower but more compatible than delaying the site opening by weeks and risking data losses everytime somebody modifies something trivial.
EDIT: Also the SMF Fixes mod is too dangerous, because it's a mod of other mods. I tried uninstalling everything so that Stop Spam can be installed (else it wouldn't install unless installed first, like the old Omni arcade) and then after installing Youtube, SMF Fixes install broke the forum with a blank page. If you don't know by heart the perfect order in which to install mods before this and what not to install, then you are screwed.