I use this workaround. It seems to work without glitches.
JT is your jumpthru platform.
On touched downbutton (trigger for user input) + player is overlapping at offset JT (0,JT.height/2) + platform is on floor --> set player.Y to (player.Y + JT.height * 1.2)
(These values are not mandatory, you may need to adjust them because your gfx and/or gameplay may be different from my project)