I can flash it via 'make flash_all', and load programs from https://uiflow2.m5stack.com via USB.

After editing partition_nvs.csv it will also connect to the wifi. I can also use the M5Burner to edit the wifi information. In both cases the Core will connect to wifi, but not to the cloud.

Via M5Burner I managed to "register" the device to my account, however when I keep the custom firmware it appears in https://uiflow2.m5stack.com as an unknown device (and thus cannot use it).
All the other attemps have failed to connect to the cloud (always appears are Private, never Public).

If I reflash the original firmware (without utf8) everything works as expected.

How can I have my custom firmware interact with https://uiflow2.m5stack.com via wifi too?