Cannot disable gate keeper
U need to see if the spctl is actually disabled though.
I noticed same wordy warnings when I tried same command. In my case it was disabled and the same warnings keep showing up no matter what spctl command is run for me.
To check results:
sudo spctl --master-disable
sudo spctl --status

Last line after the warnings should be:
assessments disabled

So, the command worked for me to disable and enable spctl.
Regarding those warnings stack overflow user bbum claims to wrote the error reporting code, but so far there is no explanation why the warnings are reporting on this command.
Good luck to u.