I'm not sure what the pattern is. On some threads it will take me to my bookmark, on others it takes me to a couple of posts from the end of the thread, seemingly at random 
So the bookmark appears and is visible, but I have to scroll back up the page to find it.
I'm using safari on my phone.
Sometimes it seems to work perfectly and others it's not. I don't know if the link is the section I'm positing in, the age of the thread, or what, but it's very annoying. At times it has taken me to my last post on the thread, even though my bookmark is further on.
It's probably going to start magically working now. This morning it has worked on one thread and not on another.