Some of our board diagrams, notably those published between 2005 and 2011, have started to display incorrectly on the Chrome browser as of Chrome version 64. There are no problems with Chrome version 63 or earlier, and we don't yet know why only some diagrams are affected.
There's little we can do about this, and we can only hope that Google fixes their browser as soon as possible.
If you run into this issue, we suggest using a different browser (such as Firefox). Please accept our apologies for this inconvenience, which is outside our control.
Update as of March 8, 2018: We reported the problem to Google and it's fixed in Chrome 65.