Hi @Chris Wood ,
Suggest you using General Scripts Wizard in SSMS to script out this procedure. Please change the options as below screenshot to make sure you script out all information for this procedure. Then run the scripts with a new name in SQL 2019 or SQL server managed instance, check if any error message occurred? If no error occurred, please share us the scripts of your stored procedure. We can start to troubleshoot this issue from analyzing your scripts.
If the scripts of stored procedure have no issue, you also want to ignore them in DMA, we can use the ignoreErrorCodes property. You can specify to ignore a single error or multiple errors.
<workflowSettings>
<assessment parallelDatabases="8" ignoreErrorCodes="46010" />
</workflowSettings>
Refer to MS document Configure settings for Data Migration Assistant.
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I don't think I got the dma.exe.config change right as once I got out of DMA it failed to start. I had just copied the script from the document and it has space lines and I probably got them added incorrectly. Once I renamed the file and ran the install with repair I now have a working DMA.