Thank you for playing, @alicia2022! I appreciate you taking the time to give me this feedback!
I also use Linux, but as far as I know, the performance should be similar across operating systems, since it is a web game. If it is running slowly on your computer, then it will likely run slowly even if you were running Windows or MacOS on the same computer. I am sorry for the poor performance you are experiencing though, and now that I know this, I will try to optimize the game wherever I can!
The note you are getting means that you need to refresh the web page on your browser and try again. If you reload the page, you should be able to upgrade the stat. Ideally the web page should not make you do this - in the near future I will try to make the page refresh more dynamically so that players won't have to refresh the page themselves!
I don't yet have a Discord server, but you are not the first person to ask about this! I will set one up in the next couple of days, and will make a post to let everyone know the Discord invitation link.
Thanks again for trying the game, and for your valuable feedback!