Not sure if you were able to get this resolved yet, but I hit the same issue in my lab. I was able to resolve it by resetting iDRAC using the -f option to preserve the user and network settings. Once it came back, no more virtual media. A normal reboot of iDRAC does not resolve, had to reset the configuration. Make sure to use the "-f" option and not the "all" option, doing so will put it back to factory.  racadm racresetcfg -f will reset all iDRAC's configuration to default, and preserve the user and network settings.
When I upgrade any IDRAC 9 card to firmware version 4.40 ([URL] , I can no longer manage virtual media via the racadm client interface or the IDRAC Web console.  I upgrade the firmgrade by booting from the platform specific bootable iso, and post-upgrade the iso is still attached. But I cannot detach it. Examples of attempts to detach the ISO: racadm remoteimage -dERROR: Unable to perform requested operation. From the Web console, click on "disconnect" in the "Configuration->Virtual Media"  screen. RAC0306: The disconnect operation resulted with error. Change the vConsole plug-in type to other than eHTML5 and try to disconnect again. Go to Virtual Console configuration and change the Plug-in type to either HTML5, Java or Activex. Retry the disconnect operation. Is there a fix for this? 4.40 seems to be most recent available IDRAC firmware release, so I think my only option is to roll back to a previous version. I've encountered this issue on every R740XD ( 3 so far ) and R7415 that I've upgraded to this version of firmware. Can we fix this here? Or do I need to call DTAC and open a service request? I usually only contact Dell for parts RMA tickets, so I'm not familiar with reporting software bugs.
IDRAC Firmware Version 4.40 Virtual Media Issues