I had this once many years ago, but don't remember the exact resolution.  I believe it was an old template referencing the old data source type, causing the MAS90 ODBC entry to be re-created... probably because the Repository / template wasn't created / converted properly.

What would be the fastest way to check if there was an old data source type lying around? Is there a table I can query or some sort of tool inside of Sage that would allow me to see something like that? Essentially, a quicker way than clicking and looking at every single one by hand.

I think you have to go file by file / template by template... but I can't really say for sure.  I'd try checking the Tenant Cache before and after running each report, to try and narrow it down.

Here's a link talking about the error. Looks like you may have to contact Sage Intelligence Support for the fix.

Problem Loading Data -a row with duplicates was encountered

I resolved by uninstall and reinstall at each workstation using SI.  One of the workstations probably has remnants of ProvideX ODBC connection.  When that workstation runs the SI report it recreates the ProvideX ODBC tenant connection for the company (which is a duplicate of the ODBC Driver SQL Server connection for that company code).