This question is multi-faceted and I'll try to answer the aspects as shortly and succinct as possible. I think the main problem you are facing is that you in some sense did not quite fully understand and follow the Humean insights here.
1. Hume and Kant
Hume put the position of empiricism - that knowledge can only be acquired via experience - to the extreme. He consequently got rid of all metaphysical and alleged "certain" knowledge of old and told us that there is nothing the like and that we will never be able to know anything about the real world for certain. All there is are habitual patterns of perception and how things "really are" is simply beyond us.
Kant did not exactly like that outcome. He studied Leibnizian metaphysics which basically were the pinnacle of the attempts to make classical metaphysics coherent (without losing God, that is) for most of his life. Thus, he strived to secure a place for certain metaphysical knowledge, ie. knowledge about the structure of ultimate Reality.
His ingenious approach was saying that to some extent, Hume was right to question metaphysical knowledge - insofar it is acquired directly via (sensual) experience. But if we take a look at the fact that we humans in fact are capable of sharing experience of a common world, there has to be something enabling us to do so. Some common mechanism of perception and thought, if you like. To uncover these patterns is what his philosophy is all about.
2. Kantian causality
As you might surmise by now, the thinking in the question has one major flaw: It assumes the metaphysical being and actuality of scientific insight, ie. that science would tell us something about metaphysics. That is not quite in line with Hume (or more elaborate recent philosophies), nor the methodological foundation of science itself: Whatever the status of scientific knowledge is, no matter how intricate and deep the insights are, it can and, as a matter of fact, and by all means, will be replaced by new, more intricate and deep insights and theories.
In other words: Our current theories about the random movement of quantum scale objects may be what fits best our past observations, but this does not mean that we can actually rule our that they follow what we call "causality" or that they are only a placeholder for underlying structures yet to be unveiled.
Now, Kant's causality is nothing but the way we perceive the world. But at the same time, it is supposed to be more than a mere "habitual pattern" or contingent theory. It is so basic that if it wasn't for causality and the other categories, we weren't even able to coherently form an experience of things in the world (his transcendental deduction tries to justify this claim).
As much as this approach was revolutionary, there is still ongoing research trying to entangle hard-wired perceptual patterns from culturally ingrained ones. Most of philosophy agrees that while Kant himself thought his theory to be penultimate, there is cultural and historical plasticity to a priori concepts.
Randomness is not at odds with Kantian causality. It actually is a placeholder for "we cannot make sense of it since it does not (seem) to follow causality, which we need to form a coherent experience and make sense of things". That is why we seek to find patterns in all this randomness, to make a "thing" out of objects which may be better described as fields or waves or strings or something entirely different which eludes our ability of intuition. Realistically speaking, the idea to visualise the path of an electron as singular object moving around actually runs against some basic principles of quantum mechanics.
So we basically have a twofold misunderstanding here: Firstly, you mistook our perceptions, or, more correctly, visualizations and rationalisations, of the quantum objects to be exactly how things actually are. And then, secondly, you mistook causality to be a universal property of Reality itself, which it actually isn't according to Kant, and followed that since things at the quantum level "really are" random, Kant must be wrong.
The question that really has to be asked here is whether we even can get "rid" of causality since a) it is so imminent in and vital to our lives as predictability is a cornerstone of all our actions, and b) as far as we know, quantum scale laws do not at all apply to our macroscopic world and cannot have any direct bearing in it, thus even if causality may become somewhat fuzzy there, it simply does not make any practical difference.