I've been seeing this error a lot in Mac OS/Chrome in the last 24 hours or so, on goal detail pages.
Thanks for reporting this! I was actually seeing this often on Stripe's dashboard a couple weeks ago. I'm thinking it may be a weird Chrome bug and not related to Beeminder. If anyone else has evidence either way that will be great to hear. Thanks again for letting us know; even maybe-possibly bugs are really valuable to hear about.
It seems that since Chrome updated a couple days ago, I have been seeing this at Beeminder and at some other sites as well.
I haven't seen this in a while.
If I knew of forum etiquette for closing an issue, I would do that.