Please include the modified properties of the layers you are having problems with the screenshots and give us workflow details. Please do not use the drag and drop here field. It is not reliable or easy for us to use to view your screenshots. Just drag them to the reply field on the forum or use the toolbar to embed them.
If you want to keep animation speed constant you need to create protected areas in your timeline using markers. This is covered in the Extended Graphics documentation. Without knowing your workflow in detail or seeing your comp with the modified properties of the layers that are giving you problems I can only guess that you have followed the wrong workflow.