Thanks for the suggestion. The problem is that when I’m having this issue I can’t actually connect to the plex server by going to http://YOUR_NAS_IP_ADDRESS:32400/web.
I am able to access by synology server through web access but the plex server can’t be accessed.
I was able to fix the problem temporarily by unplugging my router, unplugging my switches/hubs and turning off the server completely. I then plugged back the router, turned the switches on and then booted up the synology and it worked.