There is an older thread that discusses that error message that has some suggestions.
One troubleshooting step is to connect the My Cloud directly to a computer’s Ethernet port and run it that way for a while to see if the MY Cloud drops out when directly connected to the PC. That might help narrow the issue down to either a My Cloud issue or some weird network issue.
Also note that this subforum deals with OS3. If one has updated to OS5 (v5.x firmware) they should see the dedicated OS5 subforum for their device if they haven’t already. Suggestions that may fix issues on OS3 firmware may not work on or apply to OS5 firmware. With the OS5 firmware one should have options in the My Cloud Dashboard > Settings > Network section to set the SMB and other network protocol versions that may fix certain network access issues.
Personally if I had one device that kept dropping off the network I’d disconnect all other devices on the network except one computer and troubleshoot. I’d make sure no shares are being mapped to the PC. With a large number of network clients its entirely possible one of those clients is introducing or contributing to another device dropping out.
