I suppose the S_PLATFORM is the players ghost, with the platform behaviour attached.
The platform behaviour will not allow the ghost to enter solids. To do that it has a 'push out of solids' mechanisme build in.
As a result.
The "on collision with" wil trigger (only once) on that one little moment that the ghost lands.
And probaly also one little moment when the player walks in it from the left or the right.
The 'on overlap with" can not happen.
You have to use the 'is overlapping at offset' condition. With x = 0 and y = 10. Kinda.
I do not advise you to use the 'move forward', rather simulate the platform keys for left and right. With adjusted speed properties. The 'move forward' can lock you up in solids.