Our crack is down lower. It’s a horizontal crack passing through the bolt hole for the 3rd bolt from the bottom (see photo). So, those bottom 3 bolts aren’t doing anything anymore.
Last time I inspected it closely would have been about a year ago in La Paz Mexico, and we just found the crack during a big post-voyage clean/polish/repair effort in NZ. It doesn’t look like a real fresh crack, so it was probably like that for a good portion of our Pacific crossing.
That looks serious. There must be a flaw in the steel stock used for the chainplate. You are at risk if you sail the boat with that kind of damage. I suggest removing the chainplate and bring it to a welding shop. They might be able to weld a piece of stock over what you have or build a replacement.