In this case the bug with Widgets was reported through FBH by users that saw the problem as soon as the faulty update came down.
That is why we got a fix relatively quick the next day.
The users that checked the MS Store for updates got the fix the next day, but not every user checks for MS Store updates on a regular basis. It is just something to keep in mind when dealing with Apps issues. 🤷♂️
On this point about checking for apps updates: I did just that today. Without doing anything other than looking into the MS Store library, I saw that many apps had been "modified" moments before. It looked like others had been updated on the same day as the cumulative update. I kind of expected things to work this way and yet my Experience Pack had evidently not been updated like the rest.
The faulty Windows Web Experience Pack 5100 came down a little later than the cumulative update, depending on when the users did the update, they may have hit the bug or not. The fix came down a day later with version 5300 and later 5400. 🤷♂️
There is also a setting to do the updates automatically from the store, but you never know when it happens. 😎