I'm using a POST hook to call a third-party API. I hard to say for sure that it's not a problem with the API but I have to start somewhere...
This is likely related to our recent site performance issues. Once those are resolved, this should work properly again. Please keep an eye on http://status.bitbucket.org to monitor our progress.
They seem to be working as expected now. Thanks for your help. Feel free to resolve this issue.