Everytime I click Diff in the webui, I get that error: Can anyone help?

Thanks for reporting! I can see the team's been notified of this, and I've shared a link to this thread in case they have follow-up questions for you. Does reloading the page get you past it, by any chance?

No, and it's been doing that for a few weeks. I didn't report it hoping it was a common issue and that it was going to be resolved, but doesn't seem like it's too common. Other members of my team do not have the issue. As a workaround, I use the CLI to get the diff, but it's nice to be able to see it from the webui without having to re-run the pulumi command with the --diff flag.

Absolutely, yeah that should work. I'll see what I can find out for ya.

Do you have any news on this?

I don't see an update yet -- will ask the team.