Alright then after playing the heck out of the game and encountering pretty much all of the bugs in it (we think) this is our Bug Report - and really you only need worry about ONE of them. So first the common ones and how to fix them:
For reasons we cannot determine every now and then you will lose the ability to dive underwater. When this happens you can swim all you want, you just cannot dive. The only way we found to fix this was to save the game and then load the save. That seems to reset that bug.
This is another odd one that crops up seemingly randomly. It comes in two forms - pieces of the landscape that will trap you, and the game allowing you to climb into a area that you cannot then get out of.
When you get hit with this and you simply cannot get free the ONLY option is to load a checkpoint save. Yeah you may lose some progress but that is the price you pay. What you do NOT want to do is save and load because sometimes the game will save you in the stuck place. Just saying.
And now for the one you MUST AVOID at all costs!
North of Lindenvale over the bridge there is a Person In Distress Cage that has a merchant in a cell in a building there. The area is guarded by bandits, and the bandit captain has the key to the cell. BEFORE you try to get it you NEED to save your game.
The reason for that is that sometimes the captain de-spawns. And sometimes he is there but does not have the key as loot.
To be clear you NEED that key because the merchant in the cage here is one of the ones you MUST free in order to collect all of the Gwent cards. Failing to be able to free him will bug the Achievement: Card Collector (15g) Acquire all Gwent Cards available in the base version of the game.
Let us repeat that - if you get hit by this bug you can NOT unlock that Achievement! So you want to reload your save and try again and KEEP doing so until you get the key. Once you HAVE the key and HAVE released the merchant then you want to escort him to the village he sets up in to be sure he does not get killed by a monster.
Once he is set up play him and get his card and you will have missed that bug!
Some of the Bartenders and Innkeepers as well as Merchants and Traders will have Gwent cards to sell you. It is critically important that you purchase ALL of them BEFORE leaving their region. The game can and will remove the cards from their inventory if you don't - and when you go back for them they are no longer for sale.
If you get that bug you cannot unlock the Achievement for Collecting all the Gwent cards. Fair warning mates.