OpenBazaar version 1.x is currently down for updating.
The present version of OpenBazaar relies on a few federated Libbitcoin servers, which are Bitcoin full nodes, to interact with the Bitcoin blockchain. This was a remnant of when the project was DarkMarket. Unfortunately, after the recent SegWit activation they had issues and became corrupted. They are now resyncing the blockchain, which takes quite a while, but they should be caught up this evening.
To avoid similar problems in OpenBazaar version 2.0 we not only made the decision to move away from Libbitcoin but from servers entirely. 2.0 contains a peer-to-peer wallet that connects directly to nodes in the Bitcoin network. This removes the need for us to run infrastructure and removes a potential source of outages.
Thank you for your patience and we apologize for any inconvenience this has caused.