I know this issue is quite old and marked as solved, but it isn't solved for me. I have the exact same issue. The simulator slows down and down, clearing the text in the console help to get a little faster, and after a while, doing what @WolfWings said to get the simulator back to speed works.
I have this problem in chrome, but also with the steam client. I think this issue is not quite resolved. Thanks for your help
Same here. Slows down to unusable speeds until I click the cog and click okay.