Welcome to the forum.
How are the Titles being used, as Clips on Video 1, or as overlays, on say Video 2, or above?
Can you post a screen-cap of your Timeline, so that we can see the Titles?
Do any of your Titles show, or are all of them just missing?
While I have never had any "disappear," I have had a few animated Titles display in an initial "jerky" fashion, with streaming media, like with YouTube, due to buffering on the download for playback. The "trick" there is to start with say 02 sec. of Black Video (created with the New Icon in the Project Panel), and then do a Cross-Dissolve, or Dip-to-Black, from it to my Title. This gives time for the initial bytes of the file to be buffered, on the viewers' computers. Their download speed can play a role in this too, as can the speed of the server from the streaming source. However, that is quite different, than what I think you are describing.
Good luck, and let us see just a bit more,
Hunt
When i upload my video on youtube the titles disappear. I don't know what i can do 
Can anybody help me ? 
