Bitcoin's price has climbed back up to around $12,800 as of the time of publishing, and Coinbase noted that buying and selling may still be blocked. The latest update on the site's status page, which went up at 11:35 AM ET, reads, "Due to today's high traffic, buys and sells may be temporarily offline. We're working on restoring full availability as soon as possible."
Coinbase had disabled buying and selling yesterday at 5:57pm ET according to its status page, but that issue had been resolved within 15 minutes, with no indication of cause. While other occasional temporary blocks in the last month have been logged, the last few days have seen an uptick in holds put on bitcoin, bitcoin cash and ethereum. Some of these incidents weren't explained, while others were explicit processing delays due to high transaction volume.
Update: As of 1:44 PM ET, buying and selling bitcoin on Coinbase has been re-enabled. An update on the exchange's status page says the team is "monitoring for stability."