This is a common prob. Seen it many times before in UDK / UE4.
There are good reasons why it happens too, but yes its annoying.
Why does it occur?
Moving platforms often just use interpolated movement, rather than full-physics etc.
Whereas Pawns tend to use physics, as do jumps, so there’s velocity / physics too.
Even if a jump is interp’d, its not in sync with a moving platform with nothing to fix it!
A jump is often still executing as the platform moves into it which breaks everything.
1. Ensure the platform / lift uses physics, and test if it also needs to be ‘powered by physics’.
So in short, make it behave like a Rigid-Body that can push the player around or backwards.
2. Ensure all Mesh collision options and general Query Collision options are set correctly.
Why? At very slow platform speeds (test it) the player shouldn’t go through the bottom mesh.
3. Disable jumping. Probably not what you want, but consider it, as its the easiest solution.
4. Account for the jump in the movement of the platform: custom jump code etc.
Basically you override default jump code to detect if the player is on the ramp, then do a custom jump.
In UDK you could check if the player was ‘based’ on the bottom lift mesh and then test if the lift is active.
5. Use a physics volume with gravity to anchor the player to the lift (you get a short little jump)
6. Attach and lock the player to the lift. If jump is pressed then free / unlock the player.
In short the lift and the player become one movement, until a ‘jump off’ needs to occur.
(Disable physics first but then use physics to bump player off for the right visual effect)