What are the most common causes of a skipping chain on a Shimano Ultegra groupset, and how can you determine whether the issue lies with the chain, cassette, chainrings, or derailleur alignment. Does a worn-out chain always need to be replaced, or can it be salvaged by adjusting the limit screws or B-tension on the derailleur. Are there any specific tools or techniques required to diagnose and fix a skipping chain on an Ultegra groupset, or can it be done with basic bike maintenance knowledge. Is it possible to fix a skipping chain without replacing the entire chain, or is it a waste of time trying to troubleshoot the issue. What are the consequences of neglecting to fix a skipping chain, and how can it affect the overall performance and longevity of the drivetrain.