The field of epistemology is ancient. The problem of what can be known and how we can know is even older. I don't think this conflict raises any fundamentally new questions on an epistemic level.
Epistemology hasn't changed; but the engineering of how one ensures they are probably reliably informed sure has.
On the flipside, we have a lot more information about how brains tend to process and weigh information to form beliefs.
There are plenty of philosophers that rejected the idea that objective consensus is possible, even more so when faced with assigning a truth value to arbitrary phrases. Off the top of my head, both Hume and Kant noted the impossibility of true posteriori certainty. You're quite correct that this is well-tread territory, but you're wrong to think that there's some widely agreed-upon, well-defined theory of truth or knowledge.
Pragmatically, we're completely immersed in floating signifiers and appear to rely on them for fundamental communication, so I'm more arguing for a move to discussion of degrees of certainty & consensus rather than a binary understanding of knowledge.
(...and this is even before diving into gettier problems!)
The concept that needs revising is our understanding of social media posts as being automatically considered 'facts'.
If it can't be proven, if we can't trust any vehicle to independently verify its veracity, then we simply have to check as many sources as we can and consider it as a possibility, not a fact.