Comment 3 for bug 1820843

I get this issue (it seems it's the same) with snapcraft 4.4.2:
"""
Launching a VM.
                                                                                                                                                                                                                                          Skipping pull a1fbox (already ran)
Skipping pull blocker (already ran)
Building a1fbox
/root/parts/a1fbox/install/usr/bin/python3: No module named pip
Failed to run '/root/parts/a1fbox/install/usr/bin/python3 -m pip wheel --no-index --find-links /root/parts/a1fbox/python-packages --wheel-dir /tmp/tmpmx7gav05 --requirement /root/parts/a1fbox/build/requirements.txt': Exited with code 1.
Run the same command again with --debug to shell into the environment if you wish to introspect this failure.
"""
doing a snapcraft clean fixes it.