Hi,
it seems that the environment is either cleared to greedy with su -, especially the $PATH variable, or that the path of apk has changed in the meantime, which is /sbin/apk now.
I receive the following error when building on arm.
/usr/bin/abuild: line 1233: apk: not found
>>> ERROR: nginx*: create_apks failed
>>> ERROR: nginx: rootpkg failed
I fixed this temporarily by dropping - from the command and won't expect any problems with the parental environment here -- the $HOME variable is also set the beginning.
Hope that this info can help. Cheers