To clarify, my colleague responded that "rollback wasn't configured with this game". Normally, rollback is set up automatically once a new version is added to the system. In this case, I'm pretty sure the patch for Raiden Legacy got added way before rollback in Galaxy went live.
My colleague then described a workaround - downloading the offline installer without applying the patch afterwards.
In hindsight, he should have described the root cause in more detail, though. Sorry about that.

That being said, I will ask our techs if they can set up Raiden Legacy manually, so that the update can be rolled back. Since this patch is unusual in that the previous version works better for some, it would make a lot of sense to let Galaxy users roll back to it conveniently.
So thanks for bringing this up, and please forgive any inconvenience caused in the meantime. :)