I left some code running with some simple physics and noticed that a bouncing ball got higher. This was on a hardware device and my first guess was that it was something to do with imprecision of 32bit floating point. However, I left it running in browser and I think it degrades at a very similar rate if not identical.
Leave https://makecode.com/_53r2UfCfzJ7x running for a few minutes and you should notice the balls get higher and higher and eventually bounce off the top wall. This is in Chrome 78.0.3904.108. Would be useful if someone else could confirm this, it could just be my balls are bouncier than others.