flask.cli.NoAppException: Application crashing
This error may be a sign that an import is not found. To see which import is missing, try to run your server.py file with the python interpreter:
python yourapp.py
Example of output :
Traceback (most recent call last):
File "yourapp.py", line 4, in <module>
from flask_httpauth import HTTPBasicAuth
ImportError: No module named flask_httpauth
Source (and other leads)
The issue was that some package were missing or corrupted.
I reinstalled everything with pip3 install -r requirements.txt --ignore-installed
and now it works fine.