Check out that screenshot. I found this while testing the game to look for some reported bugs. It happened when I fell in the magma while the scene was still reloading. It should be fixed now, I added a patch that disables player movement while the scene is reloading.
On the other hand, Astronaught has a massive problem with memory leaks. It doesn't look like everyone is experiencing them, and I sure didn't while I was developing the game. But when I started testing in Firefox, which is what a lot of people who reported lag said they were using, the game crashed for me a couple times. This never happened while running it in Google Chrome, at least for me. There was a bug that slowed the game down when Oxygen runs out, but I think that was specific to that scenario, and I'm pretty sure I fixed it (I hope I did). So I'm not sure if the browser has anything to do with this other lag.
It looks like the same issue I had a while back with my other game, Darkhouse. I first released that game as a Flash game because I could never get it to work in HTML5 for the same reason, it kept crashing and freezing. When browsers like Chrome started disabling Flash by default, I had to upload an HTML5 version of Darkhouse, and the bug mysteriously disappeared. I have no idea how that happened or how I fixed it. I'm not even sure if it's still fixed right now.
From what I can tell, the problem is caused by drawing things like text and boxes, things I use for user interface, for extended periods of time. So I've added an option on Astronaught's home screen to switch on a simplified UI that draws less of those things. While it's on, the oxygen bar is instead just a single line of text, the paused screen is also one line of text without the box, and when you run out of oxygen, the game won't draw black boxes to fade away. These changes probably won't completely eliminate the memory leaks, I still had a crash while testing them in Firefox. But my hope is that they will at least help a little at easing the lag.
Also, remember when I said I thought I fixed medals? Apparently they're still a little broken. A lot of people aren't unlocking them even though they should be. They're still getting the in-game notification, which triggers right beside the single line of code that should be unlocking the medal. Yet the medal remains locked. I have no clue why this happens, and at this point I might just be done with medals altogether. I just can't seem to get them to work correctly. So any future games I make that would have achievements of some kind will be in-game achievements only.
I really hope the lag fixes help somewhat, because I don't know what else to do. The only other thing I can think of is to wait for Stencyl to release a build which fixes the problem. And if you just can't seem to get a medal unlocked, I'm sorry, I just can't figure out how to solve that problem. It's frustrating because I want to reward people for reaching milestones and finding easter eggs, and the issues that prevent people from unlocking those rewards, as well as the ones that inhibit people from playing the game, are simply unacceptable. I would never release a game if I knew they existed beforehand, and I don't want to release any new games until I figure out how to fix them.
For now, I'll still keep a lookout for new solutions to these bugs, and for any new bugs that I can actually fix. I'm still very bad at coding, though, so I can only say that I'll do my best. You might be able to run Astronaught better in a different browser if the one you usually use isn't working well, but I can't guarantee that the lag will disappear. I really appreciate that you all have brought these problems to my attention as well, and that you've played and enjoyed the game despite it's many flaws. It was still released better than Darkhouse and it's dastardly control scheme.