HUM-WF drops stops responding to MODBUS over Wifi

HUM-WF, Version30, Hardware Version 31, Firmware Version 11.8.

I have the sensor correctly configured for WiFi, and can be reached with T3000 and other ModbusTCP clients just fine. However, after some variable length of time with no connections (usually > 24 hours) the HUM-WF will not respond to Modbus messages. I can ping the device and get a valid Ping response, but nether T3000 or my other ModbusTCP clients can read the registers. Restarting/power cycling the device restores the proper connection operation. Please advise how to resolve this.

Thanks in Advance!

Steve