I'm going to take this couple of days silence as people trying as diligently as me to get this problem fixed
Thank you all in advance for your hard work!
EDIT: Also, if anyone needs a translation of my cap, I'm happy to help, the problem at the moment is occuring in the 'Movement' group.
The layers values 'xVelocity' and 'yVelocity' are how many isometric 'pixels' along their respective axis the object will move next tick. For slower speeds, this value can be less than 0.5, which is why it's getting rounded down at the moment to 0, equating to no movement.
Once again, my intention is to make the objects move with no fractional pixels, support slower movement speeds and have pixel perfect collisions. I'm hoping someone more mathematically minded can help me on this one