I don't think we can or should fix this.
Even in Classic, using animated sprites as your platform object is notorious for causing unintended problems. The usual thing to do is have an invisible solid square representing the player, which does not animate, and you position your animating player on top. Otherwise, you end up with lots of complicated situations like: you're standing next to a wall, the animation frame changes, and now part of your character is embedded within the wall. This kicks off Construct's 'push out of solid' code, which usually works but sometimes doesn't do quite what you wanted (your player may teleport a short distance or appear to "glitch").
So even if we fixed this, you're still going to have problems if you use the animated sprite with a platform movement. For the record, 'Is on floor' works by pushing the player down 1 pixel and seeing if it overlaps a solid there, so if your player's bottom edge raises it won't count as on the floor any more. (If you could change hot spots, you could also fix it by having the hot spot at the bottom-middle edge.)
So I think this should be resolved "won't fix".