Usually this turns out to be a defrost issue and possibly a bad defrost component that needs to be replaced. Even if you dont see the heavy ice or frost, the cold coils behind the inside rear wall in the freezer are iced up, making the cold not able to get to the fridge side efficiently.
I will recommend defrosting this one for 24 hours with the doors open so it can fully defrost properly.
Then it will likely work fine for a few weeks and the condition may not even re occur.
But if it does, all you need to do is contact me and I will walk you through the tree parts I recommend you replace at that time.
Once you rate my service kindly, you will have free access to me for 30 days, so we can be sure its all ok.
The only other thing this could be, and it is rare, is a bad or broken fan blade inside the freezer behind the wall.
In any case, I will stick with you until this is complete.
Please rate my service kindly.
Also it is the only way I am credited for my time and expertise with you.
Once you rate, I will be notified and will add your question to my priority list so you can reach me anytime until this problem is solved.
Then you can reach me by simply replying to this message anytime.
Thank you and have a great day!