I'm sorry you had to restart your run :( I honestly have no idea why this is happening, it's very very odd. I will be doing everything I can to fix it!
Edit: I rolled out another update regarding some stat issues. I haven't found the cause of this yet, as I haven't been able to recreate it.
From the very limited information about it online, it seems to be a limitation on your browser, which causes the runtime to corrupt, if the tab has been left running for a while. I'm actively looking for a fix here, but it's not easy honestly, as I have no idea why this is happening