Hi! Just faced with the issue with Bitbucket cloud webhooks. At webhook status page I see error 500 and in Jenkins logs I see:

WARNING o.e.j.s.h.ContextHandler$Context#log: Error while serving https://jenkins.my.domain/bitbucket-hook/
net.sf.json.JSONException: JSONObject["username"] not found.

After quick investigation I recognized that Bitbucket depricate and remove username field from the api request. More details here:

https://developer.atlassian.com/cloud/bitbucket/bitbucket-api-changes-gdpr/?_ga=2.164415676.2088283489.1559219877-1322535506.1557927444