I currently cannot progress the story, because I need 300 Total Power.

The problem is, Train with Sandbags only lets me hit once. Then everything other than the timer freezes, and I have to wait a minute for it to end. Afterwards I get next to no experience.

I'm playing on a Chrome browser

I tested on Windows build and it works fine (Both with spacebar and right click), unfortunately the webgl build stores save data differently so I'll have to play through the game up to that point to test out if it's an issue occuring only on WebGL. I'll let you know once I have tested it. In the meantime, make sure you're not somehow alt tabbing out of the game's window since the game stops running when it's out of focus. If you tried with spacebar, try with right click instead and see if it makes any difference (Use fullscreen too, and in general make sure the game's window is in focus).

I tested on WebGL and encountered the same issue, I'll look into it and try to solve the bug.

Thanks for letting me know!