Hello, I read that with Dawnguard installed, when you are on stage 4 vampirism people are no longer hostile to you, however, I am currently on a character that is on stage 4 of vampirism and everyone is aggressive to her. She became a vampire normally, that is, she is not a Vampire Lord/Lady. (Does that make a difference? If so, is this a bug? Any way to solve it?)

Thank you for your time,

Time is an illusion.. Just like this DLC.

To answer your question, I believe this is a simple bug. Become a VL, get cured, then become a regular vamp and see if the problem still exists.