I’ve found a glitch where if you’re jumping and your sprite hits a platform on it’s edge (at the last point of your jump) you fall through the platform below it as if it’s not there. This happens if two separate Jump Thru platforms are butted against each other too.
I can consistently reproduce this jumping in either direction. [Drop down is set to off and grab ledges is set to off].
I’ve uploaded a quick video illustration and this test project.
I can consistently reproduce this jumping in either direction.

https://drop.devloprog.org/r/3YsG6XY7rH#WR0c7Awd7HHcCIYv8Q4WqKultMdSgpwbCsAoeSzdK+c=
I’m using the latest release of GDevelop [GDevelop 5.0.127 based on GDevelop.js 4.0.99-0-release] (tested on three mobiles [all Android 11] and two PCs [Windows 10] and get the same results.