Sometimes fixing an error in your application is easily fixable by upgrading the package that has that error (if you can pinpoint the package that is responsible. )
I ran into an error today working on my course platform and I could not figure out the cause of the error.
After about half an hour of research, I found someone suggesting to update the package and that finally solved the issue. All other solutions did not work for me.
So remember to always update your packages.
Granted it was only from 3.4 to 3.6 but still.