This is the lot next to the library, I replaced the original Maxis house with the one from the Gallery. I'm currently playing and every night a vampire appears as a vampire invasion and stands there wonderingly moving in front of this house
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I tested on both residential lots near the Strangerville library and I can't replicate. Both Vlad and Lilith broke in just fine.
Vampires standing around can happen if they're the doorbell ringers and they're waiting to see if you'll let them in, or if there's a locked door in their way and the vampire can't route to you. I'm not sure what's happening in your case.
I will keep an eye out, though.