First, I just checked something and found out that the line
LBG_update_progressbar(lbg_splash_progressbar);
is totally unnecessary. This is not directly related to your problem, but updating the progressbar at this point is bad for the performance.


I don't know what you changed, but if it makes the event only be executed once, it may indicate that your level does need only one frame to load and the event was executed more than once per frame for some reason. But I can only guess that, because I don't know what you changed.