Coop Issues, enemies respawns and vanishing loot

I was playing online with a friend and without warning the difficulty went from 5 to 10. Enemies seemed to triple in hordes, and unable to clear maps before the map resets and enemies have respawned. Just 2 minutes into an area and the map starts clearing your areas already searched. Enemies respawn so fast it becomes very difficult knowing were you have been and have not been on the map. Also loot vanishes almost instantly after it hits the ground. We were unable to get to the loot fast enough to pick it up once it dropped. Also noticed a huge increase in hard to kill enemies across the map. Many that takes several minutes to kill just one or 2, and im not refering to mini bosses. This started when we where in the middle of the bone pit. Something happened, and it became so hectic and relentless that there was no moment to breath or relaxe. Swarms and swarms of enemies poured in non stop to the point that it was so hectic and stressful that the game lost all fun. Its one thing to have a difficult time with the game because its suppose to be challenging, but this went beyond that point. This is the first time that this has happened in the many hours that we have played.