We changed the DB Compat mode on our content databases post upgrade and migration. Moved databases from SQL2016 to SQL2019 and upgraded to SharePoint 2019. After migrating and finishing the upgrade many of our content databases were still in SQL Compat Mode 130(2016) so I changed them to 150(2019) and didn’t think anything of it as all of our components should be SQL2019 compatible by Nintex Standards they support whatever version of SQL your SharePoint environment supports.

Later today I received notice that one of our workflows was not working. Looking through the logs I found this error: “Query processor could not produce a query plan because of the hints defined in this query. Resubmit the query without specifying any hints and without using SET FORCEPLAN.” 

Knowing that I had changed the compat modes of the content databases yesterday I went straight to the content database the users were having issues with a Nintex form and workflow. Set compat mode back to 130 and manually fired the workflow again after cancelling the errored workflow and it went through just fine. For test I put the database back to compat mode 150 again and manually fired another failed workflow and it errors. Again set the database back to 130 and it works as expected. 

We are 100% on premise. SharePoint 2019, WIndows 2019 servers, SQL 2019 all up to date and latest CUs.