happens in the cave of evil eye 2 on the same looking platform

Confirmed, and thank you for the screenshot - the spot is clear from it.

Note this one is NOT the same as the jump-into-a-wall reports: you are describing dropping through the FLOOR you are walking along, not passing through a wall face, so the wall fix that went out does not cover it. Leaving it confirmed rather than fixed for that reason.

If you get a chance, it would help to know whether it happens at one particular x on that platform or anywhere along it, and whether walking left-to-right does it too or only right-to-left as described.

Fixed — and it was never really about that platform.

A foothold with x1 === x2 is a WALL. It has no horizontal extent, so the surface interpolation collapses to y1 and hands back the wall's endpoint as if it were floor. The failure needs a platform whose end lines up with a wall's x — which is just what a platform edge looks like — because a 1px slack makes both match at the seam. Step one pixel past the floor's end and the wall is the only remaining candidate, and its y can be a whole platform lower. That is your drop.

It only happened walking one direction because the wall sits at one end of the platform. Cave of Evil Eye I has 35 wall/floor coincidences of exactly this shape (the map data itself is fine — 609 footholds, no broken links), which is why it showed up here first, but the bug was never map-specific.

Two of the engine's ground searches already skipped walls. Three did not, all in the player controller: the walking ground-follow (the one that got you), the platform-at-point check, and the one that reads the standing platform's no-fall-through flag — that last could hand back a wall's flags instead of the platform's and let you drop through a platform that is supposed to block it.

The test pins the rule rather than this map, so Evil Eye II/III/IV and everywhere else are covered by the same check.

On develop as 9f42e4a1.