With the release of iOS 11.3.1 last week, Apple has stopped signing iOS 11.3 meaning that iPhone and iPad owners can no longer downgrade from the latest build. Long time Apple followers will know that this is normal for the Cupertino company to do after a release of an update or major version of the platform.
For the majority of iOS users, the removal of 11.3 won’t be a big deal. Most owners don’t downgrade after an update unless there are bugs or other use impacting issues. With virtually none reported, it was just a matter of when Apple stopped signing it.