There were some issues on the EU megaserver over the weekend that caused loading and login issues for players. If you're still having issues with lag and invisible mobs you can try the following steps.
From the PlayStation Dynamic Menu, navigate to Settings.
Go to Application Saved Data.
Click on Saved Data in System Storage
Select "Delete"
Select The Elder Scrolls Online.
Place ticks next to ESO Save Data.
Select [Delete] and then select [OK] to confirm your decision.
The problem is within the instances. If you lag at the beginning of the instance it means everyone will. However, resetting the trial usually makes it disappear.