Windows 10. I’m on PL5.1.1 build 4696 and today I have been offered 5.1.2 build 4700.
The download went without error and gave a file size of 811,421 KB. However, when I ran it, the installer failed, saying the installation was interrupted, except I didn’t interrupt it and the installer was the only application running. Rerunning the installer gave the same outcome.
A redownload of the update gave a file of exactly the same size but this time the update completed successfully.
Just so you know that your issue isn’t one that affects everyone - I downloaded the 5.1.2 Build 4700 (same size as you state) and it installed first time without any problem.