ADDITIONAL SYSTEM INFORMATION :
OS: Windows 10 Pro N, Version 1909
Env:
 - PROCESSOR_IDENTIFIER: AMD64 Family 23 Model 113 Stepping 0, AuthenticAMD
 - OS: Windows_NT

A DESCRIPTION OF THE PROBLEM :
Adding StandardCopyOption.REPLACE_EXISTING to the Files.move() method leads to a silent fail (i.e. without any exception) if
- both source and target are pointing to files on a special file system
- the target already exists (i.e. must be replaced)

An example file system is Google Drive File Stream (GDFS).

Side note: This can be easily tested with the jshell.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Create files `foo.txt` and `bar.txt` on a GDFS volume.
2. Write "Hello World" into `foo.txt`
3. Move `foo.txt` to `bar.txt` via Files.move() with flag REPLACE_EXISTING

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Successful move (`foo.txt` is not present anymore, `bar.txt` contains "Hello World") or IOException is thrown
ACTUAL -
Move fails without Exception, i.e. `foo.txt` still exists and `bar.txt` has a size of 0 Bytes.

---------- BEGIN SOURCE ----------
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.StandardCopyOption;
import java.nio.file.StandardOpenOption;
import java.nio.file.attribute.BasicFileAttributes;

public class Test {

public static void main(String [] args) throws IOException {
//pointing to a Google Drive File Stream location
Path root = Path.of("L:\\My Drive\\");

Path foo = root.resolve("foo.txt");
Files.writeString(foo, "Hello World", StandardOpenOption.CREATE, StandardOpenOption.WRITE);

Path bar = root.resolve("bar.txt");
Files.createFile(bar);

Files.move(foo, bar, StandardCopyOption.REPLACE_EXISTING);

//this should fail
Files.readAttributes(foo, BasicFileAttributes.class);
//this should be non zero
System.out.println(Files.readAttributes(bar, BasicFileAttributes.class).size());

}

}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Delete target if it exists ( e.g. with the Files.deleteIfExists() method) before move operation.

FREQUENCY : always