When using mobile, you are entering the title into Facebook App, right?
Using OBS does NOT send a title along, just a video stream.
You enter the title at Facebook like always, using /Live/Producer or the new(er) Content Creator??
I always use Scheduled Live Video events at /Live/Producer, so I enter the Stream title in advance (and get open URL that non FB users can watch). Oh, and for Security 101 reason, I don't use a Persistent stream key, so I'm grabbing that video's unique stream key while I'm at /Live/Producer to put into OBS
All of the above is covered at Facebook's documentation on live streaming