You're definitely not alone. From what I've read of the UKCAT (what the UCAT is based on), the consensus is that AR is generally regarded as the most challenging section. I've similarly found it the hardest by a country mile, and far-and-away the most difficult section to improve. But from my own preparation, I've seen it is definitely possible.
At the end of the day, there are probably only ~50 rules, and a finite number of combinations of these. The more you practice, the better you'll internalise these rules, and the easier they'll be to spot. It's truly just practice-practice-practice. Even if you can't ultimately find the answer, you'll improve tremendously at making informed guesses. Not only are the questions difficult, but there is enormous time pressure here. 55 questions in 13 minutes means you'll often need to make decisions that are without deep and thorough analysis!
It is an extremely discouraging section to improve at, requiring an enormous investment. Quantitative and Verbal Reasoning you could prep for sufficiently in 10-15 hours each. AR you could spend 5 times that, and still get every 3rd of fourth question wrong.