Any number of things can affect your ability to handle abstraction. (Including just not being interested.) Other people in this thread will probably bring up all kinds of ideas for external forces affecting your mental capacity.

First thing you should do is figure out what's wrong. Refer to what other people here are saying. Additionally, see if your family history includes a history mental illness or degenerative medical conditions (including dementia and Alzheimers). Everyone knows someone with this, you're looking for a pattern. For example, multiple people in my maternal grandfather's family had been institutionalized and most of the family had bipolar and schizophrenia diagnoses.

And now, how to still get your job done... :)

At one point in my career, my mental facilities became so compromised, I couldn't follow abstraction. Instead of seeking help, I figured out a system to overcome this.

What I did was externalize my memory. Quite literally, I would write everything I needed to paper: variable names, notes on their contents, call stacks.

Once the entire set of function calls where on paper, I could see the structure and continually shuffle things in and out of very limited working memory as I worked to understand and fix issues.

It's slow, but not as slow as you would think.