Users can also choose to download individual package installers and either use a combo update for MacOS or a standard update. The combo update allows a Mac to be updated from an earlier version of Mojave, for example to jump directly from 10.14.3 to 10.14.6, whereas the standard version must be installed on the preceding release.
You might try using the Combo Update package installer instead, which will update directly from 10.14.4 to 10.14.6. The Combo Update can be downloaded directly from Apple by following the links in the article or at the link below. 2b1af7f3a8