I am caching CKRecord on client and fileUrl of CKAsset too. Can fileUrl change from time to time? Asset / data itself is not changing.
The fileURL of an asset will not change, but if this is an asset you downloaded from the server the data is only guaranteed to exist at that location until the completion block of the operation is called. After that point the asset's backing file may be cleaned up at any time to free up disk space.
After downloading an asset from the server you should move or copy the backing file to another location in your application's container if you'd like to keep it.