Sudden modulenotfounderror: 'dash' - worked yesterday not today

Ok I got it working but in order to do so I had to reinstall the dash components I was using. I don’t understand what changed between yesterday and today.

I used the information in topic:

and used that pip command to install the dash components.

I am concerned that whatever happened that caused my dash components to get lost on my development PC will happen in production. Any thoughts on this?