I'm not sure when this started happening. Perhaps after upgrading to Catalina 10.15.2.
After the Indigo server has been running for a day or two all commands will fail with no acknowledgement. If I open the client app on the mac I can see that the command is sent in the 2413U status window but apparently never received by any of the devices. Restarting the mac will correct the problem for a short time before it recurs. I know that scheduling a nightly reboot of the mac would probably avoid this issue but I would rather fix it if possible.
Indigo Server 7.4.0
macOS 10.15.2
Mac Mini late 2012