I'm not an expert here, but I had spent days trying to figure out what caused my Physics to change when I tried it in 'fast forward' (higher time scale).
I still don't know why it does it (probably a bug), but I found out that it has something to do with 'World Gravity'. It doesn't reflect correctly when it comes to 'time scales' and/or 'dt'.
My suggestions are:
- Try without the use of 'dt',
- Change the World Gravity if at any point you're changing the Time Scale.
For example, if your World Gravity is set originally to 30, and if you make your time-scale to 2, then everything is messed up until you make the World Gravity to 15. Then it's back to normal physics. (so inversely proportional).
To change the 'World Gravity', you can use any physics object's action, it applies to all I believe.
And always use V-Synced and Framerate Independent (so that different refresh rates devices don't affect Physics).