Even though Microsoft's Mainstream Support End date is 10/9/2018, many enterprises have extended support policy till 10/10/2023.
- K2 releases will drop support for Microsoft products that are no longer available for standard support by Microsoft.
Was there an incompatibilty that 5.3 had to drop support for Windows 2012 R2?
We only upgrade to this a few years ago because it has been out for a while with enough fix packs to guarantee stability.
No good reason why 5.3 wouldn't work on 2012 R2. It's an incremental patch not a 6.0 major product release.