I am getting this issue as well and it doesn't matter which version of PHP I have installed. While I've had the above noted error a few times I'm usually getting a slight variation:
Fatal error: Illegal length modifier specified 'f' in s[np]printf call in /src/XF/Util/File.php on line 305.
I have been trying to upgrade to 2.2 Xenforo from 2.1.9 but the web based upgrade process fails every time mid-way through which which leaves me on a blank page where the url ends in "tools/run-job". At this point I have to restore the entire site from backup in order to get back to the admin pages. I am also having the same trouble completing add-on upgrades. Just stalls out at the run-job page. So my first question is the web based (from in the admin panel) no longer the advisable method or upgrading Xenforo? Or is there some other php issue going on here?