Speed ramping causing choppy video in 60 fps

Hi I shot footage with 60 fps and 1/125 shutter speed. Interpreted the footage as 24 fps so it's slow mo.

I want to do some fast slow or fast slow fast edits with speed ramping. I tried one with 500% (also 1000%) and speed ramp down to 100% with warp stabilizer and the footage was shot on a gimbal.

When I speed up the footage, it looks really choppy, almost like a time-lapse? Is that normal? I tried optical flow and frame blending - still the same thing. Is there anything else I can do ?

Or did I just not shoot it stable and slow enough?