That's right Shrawn.
You cannot migrate policies (xpsexport) from higher version of policy store to lower version. This is because often a newer schema would have been added which may be missing in the lower version.
For e.g in your case a new attribute CA.SM.Policy.ValidateIdDifferentUser seems to have been added in 12.52 which wasn't available in12.5.
You can check this yourself by searching for this property in all of .xdd files (e.g SmObjects.xdd, SmMaster.xdd etc)
If the changes are not much, you may be able to manually delete the unavailable attribute from the XPSExport and import it. But it's going to be tricky as it involves manual modification.