my enfj friend also says she feels uncomfortable when social gatherings are too serious. it's definitely easier for her to create a harmonious, personable atmosphere by being jokey and pleasant. most people do get freaked out when you get too personal with them too quickly. heck i've resented that social norm and tried plunging openly into potential friendships with an infj and entp..ultimately scaring them both away, so she's thoughtful in the sense that she's perceptive of others' receptivity and will adjust her conduct to meet them at their level. most of the people we deal with do like a bit of superficial foreplay in order to consider whether they want to have deeper conversations with you. but she's very good at reading people and if she senses you're trustworthy, she'll be quite thoughtful and attentive to the quality of your conversations.
i empathise with the frustration though, i tend to avoid her during social situations because my comfort zone is the complete opposite.
when enfjs avoid processing their darker side, i'd imagine they would feel more vulnerable and unsure about expressing parts of themselves they haven't entirely accepted/familiarised themselves comfortably with yet. what are these things they may be afraid to acknowledge/experience within themselves? perhaps fear of these is projected onto others via the knowledge of how revealing too much may be received, fear of burdening others, rejection, being too self-absorbed etc. maybe it's about being secure enough with yourself before you can trust others. actually, i really don't know. it's all just a guess based on years of being close friends, hoping you know at least a little bit about how your buddy ticks
she's also been annoyed at our esfp friend for being too light-hearted and simple-minded sometimes, feeling accomplished when she can draw some depth out of her. a few years ago she professed to wishing she was "deeper" but perhaps that would sacrifice the balance she already had with naturally falling into the local comedian niche. it's mostly funny when she asks people whether she's the funniest person they know. i didn't (and still don't) know whether she was being serious or not, probably tried to affirm truth via sarcasm or something. :/
overall i think healthy enfjs have the best of both worlds when it comes to social skills and intuitive insight. one interesting difference between us is she prefers to just feel emotions rather than think about or analyze them too much. this doesn't mean that my thoughts tend to be more constructive rather than being proactive about your vision, which doesn't have to be that complex.