Can someone please let me know what this bug means?

[Martin James]

One of our users has set up their own personal space. When they try to save a document, they get two errors.

Error 1: Error Saving Draft. No draft has been saved.
Error 2: Unable to communicate with server. Saving is not possible at the moment.

If they create a page in a different space and save it, it works. 

I've exported the below error message from the application log file:

2018-09-06 09:17:26,301 WARN [http-nio-8443-exec-3] [confluence.impl.hibernate.ConfluenceHibernateTransactionManager] doCommit Commit failed. Rolling back. Error: Hibernate operation: could not execute statement; uncategorized SQLException for SQL []; SQL state [HY000]; error code [1366]; Incorrect string value: '\xF0\x9F\x98\x8A</...' for column 'BODY' at row 1; nested exception is java.sql.SQLException: Incorrect string value: '\xF0\x9F\x98\x8A</...' for column 'BODY' at row 1
 -- referer: https://confluence.companyd.uk:8443/pages/createpage.action?spaceKey=~SMITHJ&fromPageId=41139991 | url: /rest/tinymce/1/drafts | traceId: 34ea111c48efc769 | userName: SMITHJ

[Nic Brough -Adaptavist-]

The log file tells me that you're using MySQL on the back-end, and your users have put emojis (or other standard-but-not-quite characters) in the body of the page they are trying to save.  MySQL does not support them normally, and hence crashes out with this sort of error.

Either swap to Postgres (MySQL can handle them with config settings, but those settings are not supported by Atlassian, so I can't recommend you do that), or tell your users to stop using silly characters.