Migration of financial reports not working since the May patch

Summary:

We have been migrating our financial reports to reports. This has been progressing well but we have noted that those in the test environments, that have been working well, are now returning validation errors. These reports (and books of reports) are still working OK in the prod environments so it looks as if something in the May patch has "broken" the reports. Has anyone else come across this and/or has an explanation of what has happened? We have raised an SR but are curious to see if anyone else has seen this and/or can advise what