Thank you for you help!
I updated to nightly and downlaod the headers from the beta repo (http://beta.armbian.com/pool/main/l/linux-4.14.13-sunxi/), but if I run "make headers_check" I get
make[1]: *** No rule to make target 'arch/arm/tools/syscall.tbl', needed by 'arch/arm/include/generated/uapi/asm/unistd-common.h'. Stop.
PS: I noticed that the SoC temperature, even in idle, is insanely high (70°C) and it causes throttling when loaded. From what I read this is cuased by a bad voltage regulation in mfr's implementation. Is there any quick fix to mitigate this?