Upon either entering or leaving the nether the game will get to the "loading terrain"page but then will remain frozen, at one point for upwards of 40 minutes, without loading into the chosen realm.  When the process is (forcibly) stopped (as it will not close any other way) the launcher reports an "unknown reason" for the crash. Entering the nether and leaving it is possible but this takes upwards of 15 or 20 attempts, seemingly working on a fluke. 

Minecraft is the only program being run when this happens, with it being set to a high priority on the processes. 

This has not happened with previous versions of the game. Normally loading into the nether would take only about 5 seconds.