[exim] What causes Exim to just silently skip SPF checking?

What causes Exim to just silently skip SPF checking?



It has started just skipping SPF checking silently, resulting in no SPF
header at all. And no, there is no ACL that is tripping before the SPF
check, because I have done a "catch-all" ACL which inserts a header after
all the SPF checks.

So what can it be?