Acronis True Image 2019 for Mac: update installation fails with error message "For security reasons, updates that downgrade versions of the application are not allowed"

Symptom

Acronis True Image 2019 is currently installed on a Mac.

You launch the program and it detects that a newer version of the software is available.

When you try to download and install it, an error occurs: "For security reasons, updates that downgrade versions of the application are not allowed".

Cause

Known issue with the live update.