Theres multiple things that could probally cause this behaviour. A bad/sloppy code... Bad level design, ect... You really need to give more info. Do you have any scripts attached to the level? .. If so are they template scripts or your own? When you built the level did you use snap? What do your levels consit of.. for example are their any high poly models Complex designs ect... Could also be your computer... How much ram,processor speed ect... Could all be a cause. So its really hard to say.

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