I think the adoption of the XML type was really low. For the reasons in the blog, lots of people kept XML in nvarchar/varchar columns, and just used some of...

100%

Just walk away and  ignore this type of nonsense and you'll win.

I'd upgrade SSMS, at least to 17.1 here and try again. There can be some flakiness at times with SSMS.

You should report this to MS, or give enough DDL and plans for someone else to report. They are always looking for potential regression issues, if that is what this...

Couple things, is your cert the FQDN of the clustered instance?

Here's a blog that might help: https://www.derekseaman.com/2014/11/sql-2014-alwayson-ag-pt-13-ssl.html

Or this: https://docs.microsoft.com/en-us/sql/database-engine/availability-groups/windows/listeners-client-connectivity-application-failover#SSLcertificates

You don't have a batch of source data; you have individual files. Each one needs to be read. You could bulk insert these into a staging table, then do the...

I found a reference here that notes a trigger on the CDC table causes issues: https://social.msdn.microsoft.com/Forums/sqlserver/en-US/af412328-7855-4f3c-8059-7861ac2e6531/is-it-sensible-to-use-a-trigger-on-a-cdc-change-table?forum=transactsql
There's also a note in the CDC docs that says the table...

Good comments, and thanks. Note, I'm not looking to rewrite an entire project or a huge section. Just rewrite the code (or some of it) from yesterday.

That's why they weren't in the question 😉