Hangs at edge of finite world

In the last week or so, the game has been hanging at the edge of a finite world. The music keeps playing, but the player can't move away from the edge. Closing the program and reopening it usually allows the player to get back into the world.... except when it doesn't (it hangs while building the terrain).
Not sure if this began with a recent update or whether my son just recently went back to a finite world. We are running build 399004, dated 2017-06-29. I notice the patch notes refer to a similar-sounding bugfix. Curious - is there a way to tell what date our computer was actually patched (rather than when the patch was built), i.e. logfiles from the update?