Possible cause of frame rate change upon fbx import?

I import single frame fbx files to be used as additive poses. These are exported in 60fps and whenever I import them, they would suddenly go to 30fps. In some cases, the number of keyframes would even go to 2 instead of 1. I wonder what export and import settings can cause these changes.

How many polygon is your FBX file, and do it have any Morphs?

No Morphs and around 35k in polycount.

What Graphic card do you have?
And how much ram do you have?
And 35K is a high number in polycount, you can try to make LOD in Unreal.

GeForce GTX 970, 16B RAM. I’ll see what I can do with the polycount but it’s still weird to me why the framerate changes whenever I remove keyframes. Take note that this isn’t during runtime.