Pip pre releases are set as the latest available package by puppet.
This is done by following command

pip --log /tmp/pip.log install pip==notreallyaversion 2>&1 | grep -oP "\(from versions: .*\)" | sed -E "s/\(from versions: (.*?, )*(.*)\)/\2/g" | tr -d "[:space:]") = $(pip freeze --all | grep -i -e ^pip== | cut -d= -f3 | tr -d '[:space:]'

As of time of writing i got 20.2b1
however when you try to upgrade you dont get the pre release but latest stable version as that is not tagged latest version
https://pypi.org/project/pip/#history

Thus puppet tries to correct this each time and you get a coorective change.

I think the check command should be changed so the pre releases are excluded from the latest version check. Or have the option to install pre-releases and keep the old check.

I checked and following command gave me the latest release:

pip --log /tmp/pip.log install pip==notreallyaversion 2>&1 | grep -oP "\(from versions: .*\)" | tr " " "\n" | grep -v b | sed 's/,//g' | tail -n 1