I'm been in fandom related activities for more than a decade and lately fandom has really getting on my nerves. Maybe I am just getting older, maybe not.
One of the things that pains me is seeing that the sense of community is almost lost to me with tumblr. It is a good way for people who were afraid of posting in lj comms to show their love for a fandom, also for artists to show their work outside of the comms but it is such a bad place to discuss fandom aspects and meta about shows. There is no direct dialogue and at least in the communities you were able to see the all the responses when someone posted something, now you have to look between hundreds of notes most of them not saying anything.
With LJ and dreamwidth you have the option of posting on comms while remaining a private blog which is important for many people.
Finding content on the tags on tumblr is a nightmare, specially when there are people who post their fanfiction there. How am I supossed to find your dramione fiction in a see of graphics, opinions, fanart and even unrelated posts.
Other problem on tumblr fandom is the lack of moderation. The old problem of posting ship hate on the ship tag and reblogging to insult shippers. There is no moderation like many comms had. I'm not saying that this kind of stuff never happened on LJ cause everyone knows the stories about the HP ship wars.
A problem unrelated to fandom that I have nowadays is: headcanons
Don't get me wrong I love headcanons and I have my fair share of them (one day I will make a post about them), my problem is people imposing their headcanons on other fans. And being hateful when someone has a different headcanon.