Hello!
Thanks for your additional info.
I made an update which could solve the boss problem. I also added more detailed logs if it is still unable to.
Please try the boss battle again, if it still doesn't work I would love some details of the console and/or ingame messages.
I added the option to reset stat points so you aren't pressured into stats you'll regret later, experiment and find out!
I also did some other fixes and am now looking to solve the memory leak problem, which can still occur after a longer play session. reloading the page will still fix it though.
Have fun playing, I hope you can fight bosses again!