This happens exactly after I imported the assets from the .gmez into the project, and persists until every GMlive stuffs, even the .gmez itself, are deleted from the project. The debug doesn't seems to launch properly, and it seems like create events from all objects are not executing, but that's all i can observe. Changing live_enabled doesn't work too. Everything seems fine without debug mode though, but i do heavily rely on my debugger so I can't trade live-coding for that. Any clue of what's happening here?

That is a bug with GameMaker - if you have "enough" code, the debugger can choke and skip several frames. 

Is resolved by adding an empty room in front which has an otherwise empty object in it which has

if (image_index >= 3) room_goto_next()

in it's Step event.

It worked!

I have tried on two of my projects and they seems to work fine. Strangely using (current_time >= 1000) instead of (image_index >=3) yielded a very different, buggy result where the object becomes persistent and last throughout rooms. I'll just stick to (image_index >= 3).

Thank you that was a rather quick response!