Edit in light of your added:
I think all this really tells us is that you can lock and unlock your FP5 on this machine with fastboot version 35.0.2-12147458
but the script is failing to run with fastboot version 33.0.3-8952118
So (another edit) the following suggestion may not be so attractive … hmmm
Am I right to say that platform-tools is not system installed on this machine?
Are you drawn to the suggestion to
… and the aim would be to provide fastboot form /c/platform-tools …
Edit for clarity perhaps as Adding adb path to the environment variables.