The fix for this issue is now available in the latest update (14.0.2) of InDesign 2019.
If you are unable to see the update notification, open the menu (three dots) from the top-right of Creative Cloud desktop application and click on ‘Check For App Updates’.
Once the update button is shown against InDesign, click on the button to update to Id 14.0.2.
If you face any problems with the new update, do let us know in the comments.
The list of fixed issues can be found at: helpx.adobe.com/indesign/kb/fixed-issues.html
InDesign TeamNathan supported this idea ·Nathan commented
I have also had this problem multiple times. I have already previously deselected the Content Aware Fit. Today it resized every page of a PDF randomly, I had not even made any changes to the linked file to update, I was just variously changing the size of the frame on each page when it happened.