Lag and framerate drop are two separate issues.
I experience severe framerate drop when two or more Virtuosos are in a party. Regardless of map and generally towards Zones 4 and 5. Framerate drop looks basically like the same game but in slower motion.
Lag usually looks like rubberbanding or feels like you are running against a strong wind/current. If you are bouncing around all over the place or getting damage from things you don't see, you're experiencing lag. I have been experiencing some pretty crazy lag on Ferelden Castle only, usually Zone 4 but occasionally Zones 2 and 3. At some points, unplayable and/or the game actually crashes me back to the PS4 main screen because it's so bad. Actually had a match where I used a Dragon Call on Zone 3 because everything was going smoothly, then out of freaking nowhere Zone 4 went to crazy Lag Land and crashed to main screen. Completely awesome, phenomenal waste of a Dragon Call right there. 