A small number of users seem to have an issue reaching the default node. I don't know why, but I have just added an option to select another Steem node.
https://steemit.com/steemblockexplorer/@penguinpablo/steemblockexplorer-com-update-option-added-to-select-a-steem-node
I hope it works now :)
Opened the site now, and it seems to work. Didn't change anything. Perfect!