Mining Theory: A theoretical mining based attack
Is there any known cases of this occurring


Yes, see Bitcoin Cash. While Bitcoin Cash had their "Emergency Difficulty Adjustment" algorithm in place, many miners would game that to cause the difficulty to significantly decrease and then quickly mine many blocks again to generate Bitcoin Cash much faster.


  what preventative measures could be taken to avoid this?


You could use an algorithm which does more than just the simple difficulty adjustment algorithm that Bitcoin uses. If you do something that adjusts more frequently or has overlapping windows, you can avoid this issue as the difficulty would ramp up and down more quickly to compensate for the sudden influx of miners. However, such an algorithm could cause the difficulty to oscillate and generally behave strangely, so you will want to do simulations and study the algorithm before deploying it to an actual coin.