KB4100347: It's no secret that some of the updates available to Microsoft cause more damage than good. A "new" security update for Specter belongs to the above update category.
We are talking about KB4100347 released Microsoft in July 2018, for corrections to security gap Spectre Variant 2. According to reports, some computers are no longer able to start after installing the update.
Despite the initial mood before two months, the update was released again last week to several devices. But since the KB description page hasn't been updated since July, we can't say for sure if this new version brings some changes or not.
The “new version” of KB4100347 is reportedly preventing some systems from booting and so far there is no fix except from removing the update.
Microsoft has not mentioned anything about the fact, so we cannot know the possible causes of these problems. The KB4100347 update "must" be installed on Intel systems, and some with AMD processors. But with both processors, there seems to be the same problem.