Most longfic writers write and publish chapter by chapter, and as such, we're particularly vulnerable to readers leaving comments about what they think will happen next in the story. Book authors usually only see the public's thoughts once an entire novel is out, but we see a trinkling of reactions throughout. That can be a fantastic motivation to keep going, but it can also stress us out when we see that some of our readers are figuring out the plot/twists.
But the truth is that a good twist is one that is surprising, yes, but also one that can be guessed. If there have been no clues leading up to the reveal, then the twist is only frustrating to readers. It's better if they can think back to what they have read so far and think, "I should have guessed that!"
But of course, then it also means that the twist is guessable. And as such, some people will guess it. That's ok! You don't have to change your story if someone finds out what's going to happen. In fact, it's better if you don't. Paraphrasing George R.R. Martin: "If you planned for the entire story that the butler did it, but then change it to the maid at the last minute because someone figured it out, then you wasted an entire book's worth of foreshadowing and clues."
Foreshadowing and clues can be too obvious sometimes. It's not an easy balance to master. But a reader being smart in your comments doesn't necessarily mean that you've been too transparent. It can simply mean that you did your job right.