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Here I'm using Ubuntu 18.04.

EDIT: I also have beem 0.23.9, the latest pip upgraded to.

This is strange, can you double check that you are using the newest version?

beempy about

I will test in the meanwhile beem on a newly installed machine.

Yeah, I was right:

beempy version: 0.23.9

By @holger80

EDITS:
I also have Anaconda 4.8.3, if it matters:

conda --version
conda 4.8.3

Python version is 3.7.7:

python --version
Python 3.7.7

Can you try

pip3 install -U cryptography

and report if this fixes it?
When not, please install also

pip3 install -U secp256k1prp

Finally, we've got it! It was the last one that fixed it.

And a year later, I ask you how did you fix it? :) lol... Trying one script and I can't install

pip3 install -U secp256k1prp

Getting some error

ERROR: Command errored out with exit status 1: python setup.py egg_info Check the logs for full command output.

Solved! Forget it :)
The solution was to run this before

sudo pip3 install --upgrade pip setuptools wheel

Phew! Lucky you found the solution, I forgot all about it.