Today i connected to my account after a while and when i checked my old desks to play wild mode i have seen that i have a lot of cards missing. I used to use c’thun and jade decks and i have no cards of that kind. Some of other cards are still in my account, but most of them are missing.
I have checked standard and wild and i’m in the correct account and region because i only have one account and i always play in europe.
Did you also use the filter in your collection to select the exact expansions the missing cards are from to see if they show up? I had several cases were wild cards are not displayed unless I select the correct expansion.
I did and they appear to craft
Did you also check in Twist?
Yes, still nothing 
How long did you take a break from the game? Months or years?
More than 2 years, i think.
I’m having the same issue, albeit with different cards. I left the game in 2019 and just returned this week. Several cards in my collection (which I used in a lot of decks) are missing, and the game wants me to craft them. I’ll be creating a similar post for visibility–you’re definitely not alone, and I’ve seen many other bug reports like this. It’s definitely something that got screwed up for returning players.
Don’t bother with the Customer Support team; they straight up told me they couldn’t help after a long back-and-forth.
I tried to contact Customer Support and they told me to write the problem here.
Thanks for let me know 
Sure thing. Are you missing any other cards? I used to play Jade and C’thun decks all the time (mine are all still there, I think, though I’ll double-check now), but I’m missing Northshire Cleric (of all things–like the most popular priest card of all time), Divine Spirit, and Pilfer. You should look to see if you still have those.
Brann Bronzebeard for sure. i don’t remember much more cards so i’m not sure
Colud it be that your missing cards are those from Core sets? As far as I understand the Core cards are temporarily given to players for the limited time and then with new rotation they can change the content of Core set. Brann was definitely Core last year, but he rotates out of Core this year. That means if you don´t have him in collection (not Core!) you would miss him
I’m going to guess this is due to changes in the Core set.
Do you know what the Core set is?
In March 2021 Blizzard added the “Core set” to the game, which is a large collection of cards that is loaned to everyone for free for a year. You do not own these cards and you cannot disenchant them; they just magically show up as part of your collection for twelve months.
Each year the set is changed. Some cards are removed and other cards are added.
Brann Bronzebeard was part of the Core set from March 2022 to March 2023. If you built a deck containing Brann during that time, it used the Core version by default (even if you owned the original Brann), and the deck will now list Brann as a missing card, because the Core version is treated as a different card which you no longer have in your collection.
Brann was a free temporary card.