I met just the same issues at the begining of use my Core2, but later I figured out that its just a problem of M5Burner and M5Stack project immaturity. Only UIFlow and Core2 factory test apps are compiled properly for Core2, other programs listed in M5Burner compiled for M5Stack Core and incompatible with Core2 (you can recompile they using sources and proper includes). Anyway after "bricking" the Core2 you can easly burn UIFlow or FactoryTest or another manualy compiled program through M5Burner or PlatformIO or standart ESP-IDF toolset from Espressif. Its not a real brick state, but just firmware incompatibility.