Its not bug but a workaround just in case if any one is searching for solution. I was successfully using WiFiManager with MySensors 2.3.1 but after upgrading from MySensors 2.3.1 to 2.3.2 i was unable to compile ESP8266 gateway sketch and had error

To fix this iissue you need to comment out MySensors code in two location in core/MyGatewayTransportEthernet.cpp may be there is better way but this is quick fix.

 #error ESP8266/ESP32 gateway: MY_WIFI_SSID not defined!

MySensors_2_3_2/core/MyGatewayTransportEthernet.cpp:52:2: error: #error ESP8266/ESP32 gateway: MY_WIFI_SSID not defined!

 

Comment out line 49 to 55

Also comment out line 184 to 189