-When you are in Novigrad and you are send to investigate the Fighting Pit to find Whoreson Junior, do NOT talk to the dwarves outside the entrance, they are required for the Gangs of Novigrad quest but entering the fighting pits with them will bug out the secret room/vault.
-Do not do the Master Armorer quest before doing 'The Lord of Undvik' quest, it will trigger a cutscene/moment which makes you unable to complete the 'find Hjalmar' objective. In case this does happen to you, the work around it is to travel to the next village along the road, Hjalmar will be located there and you can continue your quest.
-My game randomly decided that I did not have 'the lost miner's' DLC, not a clue what caused this (I play through Steam) but I fixed it by: Closing down the game, disabling the lost miners DLC, launching the game, closing it down again, re-enabling the DLC and then launching the game again.
-I visited an Island in the north east of Skelige, went to the town to sell some stuff since i was overburdened which triggered accepting a quest to enter a tower. The quest was level 30 so I moved on, after that my water graphics became... odd...
I loaded an save from earlier that day and my water was fine. This caused my to investigate. I managed to visit the island without issues so
I think it is related to the quest. All I can say is, make sure you hard save before visiting this island and avoid the town untill you are ready to do a level 30 quest. The town is called Urialla Harbor and the quest is called 'The tower outta nowhere'.
After having picked up the quest for the second time I did not run into the issue again, so I don't think it's the island or the quest causing the issue, all I have figured out so far is that loading a save point from before the problem fixes it.
For reference sake here are screenshots of what happened to my water:
Before:
After: