I must admit, I am a little bit confused on "arduino core" version! IDE is 1.8.5, Arduino AVR Boards is 1.6.21, ESP8266 is 2.4.1. Is that what you ask for?
As for lwip, it WAS set to V2 Lower memory, I tried both V2 Higher bandwidth, 1.4 Higher bandwidth and finally v1.4 Compile from source. Before every change, I issued a clear_flash. The first 3 show the usual (for me!) problem. The last, compile from source, fails in compilation.