I'm stuck in a loop. My primary special interest, which involves specific movies that Tim Burton and Johnny Depp collaborated on, has been going on for nearly 2 and a half years.
Overall I'm pretty tired of it; over the past two years I have seen those movies so many times that I have them memorized. But I am not passionate about it like I was when it started back in 2010 - watching the movies these days feels, as the OP described, like more of a chore than something that brings me joy.
I mostly stick with this interest out of convenience - it's what I know best and what I am comfortable with, and every time I try to go with something else, I always wind up going back to it. Besides, everyone expects me to be into it since I have talked about it so much. I'm afraid that if I tell people that my special interest has changed, then I will somehow disappoint them.
I used to feel like I would be stuck with this interest forever, but recently I actually found a couple of things that have caught my eye. I feel cautiously optimistic that they might become my latest special interests, especially since I wasn't actively trying to hunt for new interests when I found them, so my enjoyment of them doesn't feel forced in any way - it's genuine. Only time will tell if they're just another phase or if they'll become my next "thing".