i have the exact same problem . i made a post related to this . this is the link .
https://forums.unrealengine.com/community/general-discussion/1841382-what-is-this-raytracing-dynamic-geometry-update-sorry-i-m-a-noob
Its been 4 days that i am looking for a solution and the only thing that i got is this tip from Ben Cloward’s youtube channel . he said : . . .
" In order to speed up the process of doing ray triangle intersections, the engine builds a bvh or bounding volume hierarchy. For static objects, this can be done once before the rendering starts. But for dynamic objects it has to be done every frame. So it sounds like you need to reduce the number of objects in your scene that are marked as dynamic. "