The latest cumulative update (22) for SQL Server 2017 has just been released. It includes many fixes to bugs and known issues. I counted 40 of them. Here are just a few examples of interesting fixes included in this cumulative update:
Access Violation Exception Occurs in Availability Groups - This might happen when you run large log backups on a secondary replica.
Incorrect Results on a Linked Server Query - This is an interesting one. If you run a query with aggregates or joins against a remote table with a filtered index, and you don't have the VIEW DEFINITION permission, then the query optimizer considers the index to be a full unique index, and the query returns incorrect results.
Sharing Violation When You Run the "sys.sp_cycle_agent_errorlog" Stored Procedure - It's a good practice to recycle the SQL Server error log as well as the SQL Server Agent error log on a regular basis. I wrote about It here. Unfortunately, in some scenarios, the sys.sp_cycle_agent_errorlog stored procedure might fail due to a sharing violation.
Remember that starting from SQL Server 2017, service packs are no longer available. Microsoft modified its servicing model to include only cumulative updates, and you should treat them with the same level of trust and confidence as you are used to treating service packs.
Having said that, you should read the documentation and test every update before installing it in production.
You can read the documentation about Cumulative Update 22 for SQL Server 2017 and also download it from here.