Hey JmGodin,
We’re running the following config on two sites: WordPress v4.6.1 , WordFence Premium v6.2.6 and SG CachePress v2.3.11
We haven’t updated WordFence to v6.2.7 yet, but the SG SuperCache test is successful on both sites: Click to See Cache Test Image at LakePath.com
Questions…
1) Are you running the same versions as above?
2) Are you running WordFence Premium?
3) Did you disable the WordFence builtin cache function?
4) Anything you’d like me to check in our WordPress or SiteGround settings?
John