Restarting, I managed to get through the cave by not excessively grinding and only entering each floor of the cave once. Fought the aqua grunts and then they fled. When I left the cave to proceed and cut down the brush where Jorex (boy rival #2) catches up to challenge a battle, I was given the screen blackout leading to the battle, then it stays black. The trainer battle music continues to go on but nothing happens and I'm stuck with a blank screen.
The blackscreen has happened to me too and a few others and djg will have probably fixed that in the next Beta.