Can you look to see if you have KB4485449 installed in history as well? it shows in the how to get update link of that page that it helps to have that 1st -
Before installing this update
Microsoft strongly recommends you install the latest servicing stack update (SSU) for your operating system before installing the latest cumulative update (LCU). SSUs improve the reliability of the update process to mitigate potential issues while installing the LCU and applying Microsoft security fixes. For more information, see Servicing stack updates.
If you are using Windows Update, the latest SSU (KB4485449) will be offered to you automatically. To get the standalone package for the latest SSU, go to the Microsoft Update Catalog.
click on the link you gave me, and look in How to get this update section
follow steps to get the missing KB and see if the update that keeps failing actually succeeds.
Avoiding 1809 only work for 1 more month or so as 1903 due out next month and Microsoft like to keep everyone on the at least the last 2 versions of windows as they don't officially support any older ones.