Maybe your culprit is the curve tangents. If the tangents are set to cubic, they make the value go off to interpolate correctly in the curve. It’s useful when you want to have an ease-in, ease-out, but not helpful when you want to do what you’re doing.
Try to go into the curve editor for your sequence and change the tangent interpolation to ‘Linear Interpolation’ for those keyframes:
Always when i animating some paramenetrs (possition, material opacity scale paramenet, etc.) UE trying to lerp values between 2 keyframes, but when i dont need to lerp it, UE stiil going to lerp, even i place support keyframes. Example on screenshot: I need to animate opacity from 0.4 to 0, its good. but when i need a 0.4 again after some time, beetween these keyframes UE lerp goin to negative (red lines), and even i place more support key frames with 0 valuse (blue lines), opacity still goin to lerp, just closer to right keyframe. Ofcourse i can just on and off object, but this bug works with position of objects and more. As i remember at UE 4.13 and 14 there is no bug.
