Adjusting Physics substepping settings won’t make a difference here, unless platform is simulating physics.
This problem is caused by platform object moving into character without checking for any collision. Using either a timeline or matinee to move platform simply changes platform’s position without any regard as to what may be overlapped at destination. At that point burden is on character to try to resolve overlap, which it can do in some cases, but which is more difficult if it is penetrated by a large amount.
One thing that may help is to set “AlwaysCheckFloor” to true on CharacterMovementComponent. This is just a guess because I can’t reproduce issue exactly (it is sometimes very frame-rate dependent as well), but it may help with case of platform starting below player when player is standing still.