I'm sure you have seen this but just for reference:
If your Harmony Smart Control stops sending commands or the Harmony App is unable to discover the Hub, rebooting the Harmony Hub often resolves the problem. To reboot the Harmony Hub, disconnect the power cable, wait 10 seconds, then connect it again. Rebooting your router by disconnecting and reconnecting its power cable sometimes helps with Wi-Fi connectivity issues.
If the Harmony App continues to control your devices but the Harmony Smart Control remote does not, you may have to re-pair the remote and the hub.
Ensure the Hub is powered. Wait 30 seconds after first connecting it to a power supply.
Press the Pair/Reset button on the back of the hub.
Press both the Menu and Mute buttons on the remote at the same time.
Once successful, the LED on the Harmony Hub will blink green for 2 seconds, then remain solid green. If this is not successful, try replacing the batteries in the Harmony Smart Control remote.
TV Samsung UN65HU8550FXZA TS02, X-10 lighting, IR543 Powerhouse Command Ce
AVR Yamaha TSR-6750WA
BR Player Sony S6200
STB Dish 211K
SPEAKERS JM lab speakers
REMOTE CONTROL Harmony Ultimate remote