python: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.25' not found (required by python) from specific dir, but not from a copy of it

I have 2 repositories. In both I'm running a similar command (in Python's multiprocess, with 2 seconds sleep between).

The command is a python script I have, and I'm running it via each repo's virtualenv (created with python3.5)

How is it one repo gives this error and the other does not? I tried reproducing without multiprocessing and it does reproduce. One repo is flawed somehow in its libc6 search.

I pre-installed sudo apt install libc6-dev libc6-dbg libc6-amd64