You are probably suffering from two things
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UE5 does this much more than UE4, but…
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It’s mainly due to either not having enough VRAM ( >=8 is good ) or you are using too many high res textures.
Anyone can bring a top shelf GPU to its knees given 20 mins and some Megascans assets. It’s time to learn about optimization 
If you set the engine scalability level down a notch, this problem will go away.