Yes the dotted lines show a split in task work. It represents a time within the duration where there is no work. In the example you show I see where the task work is completed before the task duration (tasks 1654 and 1655). Task 1609 is an example of non-contingent actual work that was applied which leaves a gap within the duration.
To fix the first issue I suggest not using fixed duration task type. Fixed work and fixed units allow Microsoft Project to flex the finish date/duration to match work applied. the second situation displays as designed. It can be changed but a bit tricky.
It depends on what you want to do with these situations. Hope that helps, and let us know if you would like additional information.
