Hey @Wilfred_Wong,
I’ve moved your post to it’s own thread so we can take a closer look. So we can better assist you, please provide a brief description of your current setup using this link as a guide.
Make sure to describe your network configuration/topology, including any networking hardware currently in use, so we can have a clear understanding of how your devices are communicating.
Just to verify, this is the first time you’ve experienced this type of behavior? Have you tried rebooting your Core machine?
Have you tried giving Google DNS a try? We’ve seen similar reports improved by using it.
Thanks,
Dylan