ADDITIONAL SYSTEM INFORMATION :
macOS 10.14.6, Tested with Oracle JDK 8u202, 8u221 and 13

A DESCRIPTION OF THE PROBLEM :
Beginning with Java 9 it is no longer possible to call force() on a FileChannel pointing to a file on a mounted WebDAV drive (similar reports for CIFS drives on Linux that I can not confirm).

REGRESSION : Last worked in version 8u221

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Mount a WebDAV-Drive (in Finder press ⌘K). For Testing you can use a URL obtained from the upper right corner of webdavserver.com
2. Run attached test class, provide an absolute path to a any existing or nonexisting file inside the mounted drive as arg[0]

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
No exception
ACTUAL -
java.io.IOException: Invalid argument
at java.base/sun.nio.ch.FileDispatcherImpl.force0(Native Method)
at java.base/sun.nio.ch.FileDispatcherImpl.force(FileDispatcherImpl.java:82)
at java.base/sun.nio.ch.FileChannelImpl.force(FileChannelImpl.java:461)

---------- BEGIN SOURCE ----------
import java.io.IOException;
import java.nio.channels.FileChannel;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;

public class ChannelForceTest {

public static void main(String args[]) {
if (args.length != 1) {
System.out.println("Run with arg[0] being an absolute path to a webdav-mounted directory");
System.exit(1);
}

Path p = Paths.get(args[0]);
try (FileChannel ch = FileChannel.open(p, StandardOpenOption.WRITE, StandardOpenOption.CREATE)) {
ch.force(true); // fails
System.out.println("No exception under JDK 8");
} catch (IOException e) {
System.out.println("Exception under JDK 9+");
e.printStackTrace();
}
}

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

FREQUENCY : always