I've had numerous issues with IIS 8.5 becoming unresponsive, necessitating a server reboot to get the service back up and running. All FTP connections to the IIS IP are not allowed until the reboot. The only thing I see in the inetpub logs at the time of the hang are ControlChannelOpened commands with no corresponding ControlChannelClosed commands.
2020-07-03 04:40:55 ControlChannelOpened - - 0 0 103d5304-b76d-4df8-8cc9-672a7fa675d1 -
2020-07-03 04:40:55 USER tmdftp 331 0 0 103d5304-b76d-4df8-8cc9-672a7fa675d1 -
2020-07-03 04:41:02 21 ControlChannelOpened - - 0 0 63ac568f-afa9-46c2-ab8d-46b02284cbfd -
2020-07-03 04:41:02 21 USER tmdftp 331 0 0 63ac568f-afa9-46c2-ab8d-46b02284cbfd -
After a reboot of the server, the IIS will work as it should for a few weeks before expieriencing this issue again. Inetpub logs always show the same thing.