Starting next month, improved service stack updates so that critical security updates & critical non-security quality fixes blend together & get applied in the proper order. 

https://redmondmag.com/articles/2018/09/21/windows-servicing-stack-updates.aspx

Microsoft plans to release future Windows servicing stack updates (SSUs) as part of its monthly update rollups to avoid issues that have affected some Windows 7 users in recent months.

Wilcox explained the problem that led Microsoft to make this change. Some Windows 7 users were just installing security-only updates each month, instead of update rollups, which contain both security and quality updates. It’s an option they’ve had ever since Microsoft switched Windows 7 and Windows 8.1 users to the monthly cumulative update patch model used by Windows 10. Cumulative updates contain new updates, as well as past ones.

Microsoft, though, was packaging its SSUs as part of its monthly update rollups — that is, they were included in the updates that contained both security and quality patches. These SSUs were marked “critical” to apply, but some Windows 7 users skipped them anyway because they just were applying the security-only patches, which didn’t include the SSUs. However, without the SSUs in place, these Windows 7 users later found that they weren’t able to install subsequent monthly rollups. Instead, they received “error 0x8000FFFF,” Wilcox noted.

It turns out that SSUs are needed for the update process itself to work properly. Here’s how Wilcox described them: Servicing stack updates, or SSUs, are periodic updates released to specifically service or update the software stack for Windows platforms. These are fixes to the code that process and manage updates that need separate servicing periodically to improve the reliability of the update process, or address issue(s) that prevent patching some other part of the OS with the monthly latest cumulative update (LCU). Servicing stack updates ensure that you have a robust and reliable servicing stack so that your devices receive and install Microsoft security fixes.