When my arduino performs the nexInit() command i receive the "recvRetCommandFinished err " message, but the Nextion & arduino program does work as it should.
So the question is: what does the program try to tell me?
recvRetCommandFinished is status of last command sent.
bkcmd sets how much status Return Data is sent back
when 0x01 0xFF 0xFF 0xFF is received, then ok
if this is not received then err.
This is in the library code in your folder.