Is there any known observed or theoretical process by which new emotions could be observed or discovered?
Although one may argue over the exact number of emotions that exist today or the exact criteria that differentiate one from another, there is broad agreement on the general types of emotions that exist (e.g. most psychologists would agree that happiness, sadness, envy, anxiety, excitement, anger, disgust, lust, pride, etc. are emotions while pecan, horseradish, choke, stupid, chair, delta, redshirt, appoiapgpadvap, asdf, and yooe caph garharheq are not emotions). Those minor disagreements/edge cases are not what I am talking about, but a brand new emotion. Hypothetically, I can imagine that one might result from novel stimuli (or patterns of stimuli) never before experienced by humans (and thus resulting in a never-before seen affect on the brain), but I am not aware of any actual cases of this occurring or any known (outside of science fiction) theory of what sort of stimuli patterns might accomplish this or what such an emotion might be like.
If it has been shown that one of the "standard" emotions today arose after the advent of anatomically-modern humans (e.g. Cro-Magnon), I would consider that an answer.
In response to a comment by Bryan Krause, I am aware that there is a linguistic argument here. I'm imagining this as similar to the linguistic/neurological divide in color taxonomy. Famously, Russian does not have a single word for "blue" (instead, dividing it up into two separate colors), while Japanese historically did not distinguish between what English speakers call blue and green, but I believe it is fairly well understood that these distinctions happen at a fairly high level in the brain, rather than representing truly distinct forms of cognitive evolution. The color equivalent to my question could be whether it is possible for the brain to evolve, or for novel stimuli to generate, an entirely new color that no one has ever seen before and that cannot be reasonably described as a variant or subtype of an existing color. Some science fiction authors, famously H. P. Lovecraft, have tried to imagine a "new" color, so the idea that new cognitive experiences could be found is certainly not new.
Another way to ask this is whether the process of coming up with new words to describe emotions represents enhancements in the understanding of current emotions or whether it represents truly new emotions never before experienced or observed.