OK - I found the issue. Somehow missed it in all previous searches.

https://blogs.msdn.microsoft.com/sqlserverfaq/2010/09/07/open-symmetric-key-command-prevents-query-plan-caching/

Not sure what approach we will be implementing but at least there is...

Hi Sue-

Thanks for taking time to try a re-pro and to reply.
Actually, this is the issue - that it is not in the cache and therefore is...

ChrisM@Work-

You nailed it. Thx!

Needed to CAST the delimited values to the corresponding base table column data types.

I hope to return a favor some day.

Thanks again

Thx David

I read the post you cited. This is the key line from it.

"3.Use inline TVF when possible: In the demo, it’s unnecessary to use a multi-statement TVF. ...