The older view was that causality was like goodness, it was something that had no proper empirical existence. It's not like a stone in the road that one just comes across. The issue rests on some from of distinction between experience and intellect. Causality, like goodness, may have a real existence in the world, but must be derived through reasoning and is not directly available even to the "eyes of the soul." Hume and Kant destroyed, and then Schopenhauer obliterated the metaphysical certainty in causality.
Epistemology in the context of Anglo-English and the currently dominat analytic tradition is a vague term, questions concerning knowledge. In the German tradition it was a term that grew out of the post-Kantian reflection on the subject matter implied by the word Transcendental. The issue of the conditions for any possible experience (not merely for human or "subjective" experience). Kant said that the negation of the principle of causality is not syllogistically contradictory. Because one can speak consistently of an ex nihilo event (of creativity coming into the daily flow of things). Schopenhauer thoroughly demonstrated the faultiness of both Hume and Kant from the perspective of sound reason, which had not yet been demoted to the status of mere subjectivity.
When Popper introduced his famous statement of the Problem of Induction in a scientific context, which is somewhat contested in its status, he seemed to speak epistemologically in the inexact Anglo-American sense. If one tries to make his statement exact, into a formal epistemological principle, still in Anglo-British terms, the statement that one can test for conditions of falsification, but not conditions of verification, becomes meaningless (the vague notion of "corroboration" comes in as a common sense surety). Because a break in a causal chain doesn't prove that the chain won't be reestablished and then never broken again. Or, that the chain once broken won't always threaten to return to the old observed regularity. It becomes merely a working assumption wanting for the apodictic certainty of mathematical objects.
The term ontology was often used interchangeably with the term metaphysics in the tradition. And its use has become quite anarchical in our own time. The variety of uses being limited on the one hand by the most powerful thinkers, e.g., Heidegger, and on the other by the analytic philosophy departments now in control of the university proper (in contradistinction to the numerous independent actors within the university system).