They get left behind trying to work out what a previous word meant
This is one aspect of the problem above that all people speaking a foreign language have experienced at one time or another. This often happens when you hear a word you half remember and find you have completely lost the thread of what was being said by the time you remember what it means, but can also happen with words you are trying to work out that sound similar to something in your language, words you are trying to work out from the context or words you have heard many times before and are trying to guess the meaning of once and for all. In individual listenings you can cut down on this problem with vocab pre-teach and by getting students to talk about the same topic first to bring the relevant vocabulary for that topic area nearer the front of their brain. You could also use a listening that is in shorter segments or use the pause button to give their brains a chance to catch up, but teaching them the skill of coping with the multiple demands of listening and working out what words mean is not so easy. One training method is to use a listening or two to get them to concentrate just on guessing words from context. Another is to load up the tasks even more by adding a logic puzzle or listening and writing task, so that just listening and trying to remember words seems like an easier option. Finally, spend a lot of time revising vocabulary and doing skills work where they come into contact with it and use it, and show students how to do the same in their own time, so that the amount of half remembered vocab is much less