Finally figured this out, in the Python extension you have this option 'Python > Experiments: Enabled' The key is 'you MAY get included in proposed enhancements'.
All three computers have this setting enabled, looks like only two of them got auto opt'd in to the experimental feature 'pythonTerminalEnvVarActivation'
To force this feature, click on 'Edit in settings.json' under 'Python > Experiements: Opt Into' and add 'pythonTerminalEnvVarActivation'