Many perceived problems are not due to flaws in the wine but are simply a matter of taste. A wine may be too sweet or too dry for you. It may have too much of an oaky taste or not enough. It might just be lousy wine. Certain wine and food combinations can leave a bad taste.
Salads often make wine taste dreary.
Desserts or even sweet sauces can demolish dry wines. If the wine seems strange, cleanse your palate with some bread or a sip of water. Then take another taste of the wine and see what you think. Picking up problems in wine takes experience. Chances are you'll run through a lot of bottles before you'll come across one with a fault.