Hello,
i updated a Mosaic in ArcMap 10.5, since that the Mosaic is unreadable in ArcExplorer 3400 and ArcMap 10.4.x
A personal/File/Enterprise geodatabase release 10.5 can only be read in a client (ArcMap) release 10.5. Check Client and geodatabase compatibility.
If you are storing the Mosaic dataset in a File GDB, you create a GDB of lower version (say 10.4.x) and import the required datasets from the Geodatabase release 10.5.