Okay, I just got hit by this error, when I was trying to visit a friend's island. I've tried clearing my cache, an alternate browser, rebooting my PC and even using a different computer, so the problem is definitely not on my end and it seems that this list of causes is not comprehensive.
Really awkward time to get hit by this, with the event running, as I am currently holding a stash of Chocolate Rabbits to be used for balloon production, not to mention personally, as I have buffs on my coinages due to run out many hours before the script is due to run.
I figure there is no point me contacting support today as the script will run before anybody is there to give me a reply, let alone fix the issue for me.
Some bugs I understand are not high priority to be dealt with, but I do not believe it is unreasonable to expect there to be a better fix in place for an issue serious enough to prevent players from being able to play a 'real time' game than this 'workaround', especially with it being a known issue for such a long period of time.
EDIT:
If anybody on my friends list is reading this... please chuck some baskets on my coinages if you notice the buff has expired... cheers!
2nd EDIT:
Apparently nobody could visit my island. Anyone who tried got booted themselves, but was able to log back in, thankfully!
After further thought, I'm 99% sure I got hit by the bug when trying to return to my island after visiting someone elses, though I don't have many ideas as to what could have happened whilst I was away to cause the crash. I certainly wasn't building anything 'special' such as a silo or watermill. I may have been upgrading my Friaries around that time... but I am not, in any way, certain about that.