Hey all,
I'm having an issue on a PCF after updating to 1.7.2. My project builds fine, but when I run an npm start on my project, I get this error: UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'compileTime' of undefined.
Here's a screenshot with more information:

The error tells me the issue is on line 67 of pcf-scripts.js, from within the pcf-scripts package. Here's a screenshot of that line and a few relevant lines around it:

So my first thought to fix this issue was to just roll back to a previous version. I plugged "pac use 1.5.5" into the terminal, got confirmation that it moved the CLI to the correct version, and proceeded. The error persisted. I started a brand new project, initialized from scratch, put CLI to 1.5.5, and ran that project, only to find the same error.
So I looked into my package.json to find that the pcf-scripts and pcf-start modules in my projects were both still on version 1.7.2, and that rolling back the CLI didn't roll the packages back with it. So from there I ran "npm install pcf-start@1.3.1" and "npm install pcf-scripts@1.3.1" in my project and finally the npm start command ran without issue. I'm not sure if I actually had to roll all the way back to 1.3.1, but it seemed a good idea to roll back to a common version between the two packages.
Hope this helps if someone else runs into the same problem.