It did happen a lot for me as well yesterday, I suspected it was a browser problem so I switched from a firefox based to a chrome based one and it was working until it did it again in the chrome based one, it doesn't seem to be tied to a url but it first happened on creating a new assistant and than even the main dust.tt didn't work throwing this 500 error. I had to clear cash and restart the browser and it worked but it did it a gain after a while.
I'm not sure what might be the problem exactly, I'll make sure to gather more info to share if it happens again.