Hello Tibolli
I use Construct 3 and I think I have exactly same problem with my game.
When jumping on moving platform (jump through + sine) from time to time player is falling down through the platform.
Thank you for posting your solution. I understand that you have added to moving platform a solid behavior. The solid behavior is activated when player is overlapping that sine moving platform?
I wonder can you share your solution with more details? Is there a trigger? What is the offset value?
Or perhaps you could share a file with your solution or print screen? I would really appreciate that. Thanks in advance!