I think I found the problem. I think it misbehaved because of an illegal character in the "HOSTNAME". Changed the hostname yesterday and It was still alive this morning even if I have not pinged it.
This is an interstitial adapter board for connecting an ESP8266 Wemos D1Mini to a Moteino or similar wireless node (one with an FTDI header interface such as, for example, an Arduino Pro Mini or ARM board that utilize an NRF24L01+, RFM69, or similar).
The intention of this project is to provide a simple, inexpensive hardware platform for those who want to use ESP-LINK and who want to get up and running quickly without first having to puzzle over how to configure suitable hardware. ESP-LINK can provide a convenient wireless console window for debugging and interacting directly with your wireless node. In addition, it can also provide wireless over-the-air programming of your wireless node.