I am also unable to log in since last night, i refreshed due to a building not showing it was upgrading and it now gets stuck at the "tip of the day " screen no matter how long i leave it.
I have done everything from the guide i found in the forum that recommends clearing caches, checking browser and adobe are up to date etc but still no luck.
I visited a friend and tried to log in at theres but still couldnt and they visited me and can log in as normal at mine. My friend also said that they are unable to visit my island but can visit everybody elses.