According to http://lemmy-status.org/endpoints/_sh-itjust-works there has been several moments of downtime recently today for this instance, so that might be the cause of it.
Even after the health was ok it took a bit for me to be able to log in, so there might be some services that take a bit of time to come online again
I was wondering myself for a while as well😛
I even tried to search in this instance for a answer to why it couldn’t load before thinking to look for some external source