According to Apple's release notes, Logic Pro X 10.3.1 fixes a bug that caused regions to behave unexpectedly when moved, and it fixes an issue that could cause regions on Track Alternatives to get deleted.
As for feature additions, global edits cutting or inserting time are now also applied to inactive Track Alternatives, and projects that use sample rates other than 44.1kHz can be shared to GarageBand for iOS.
Today's 10.3.1 update comes just over a month after Apple released Logic Pro X 10.3, a major update introducing a refreshed interface, Track Alternatives, and Touch Bar support for the new MacBook Pro.
Logic Pro X is available for purchase from the Mac App Store for $199.99. [Direct Link]