The tiles that worked some of the time
During QA testing of an upgrade, a journal-entry tile worked on some attempts and not others. We traced it to a mismatch between the UI library on the front end and the back end. It was patched before go-live, which is the only time that fix is cheap.
The allocation that changed its mind
In the first month on a new release, a cost allocation cycle posted to a different functional area than it had for years. A user exit had been altered by the upgrade. We corrected it, tested it in QA and took it through the change board before the next close.
The hosted system that moved to AWS
An S/4HANA landscape moved from a vendor-hosted cloud to AWS. Replication, recovery documentation and monitoring were rebuilt as part of the move, so the new platform started with the controls the old one never had.