Regardless if you map through OC or through Explorer (or Drives>Map Network Drive (Winodows)) it is using the same Windows API to mount it underneath, and it maps direcly on Windows itself, so it the mapping, credentials, connection, lifecycle... are all managed outside of OC.
When you say it is coming and going, I am not sure what could be going on there as I have both at work drive mapping as SMB3 to Windows Server and a Synology Rachstation and at home to low cost Synologogy Diskstation and I didn't notice issues with it. Is just the drive not showing or it is not accessible at the moment where Explorer can still access it? Try opening directly \\NAS\share and adding that to sidebar favorites, and when it disappears, check if that one still connects. When that happens it is also worth checking Windows Event Viewer for anything network related logged into it, and I can see what I can make OC log to the log files related to drives coming/going and if there is any message attached to those events