Is any paragraph Style applied to your paras?
Did you try apply this style holding "Alt" key?
Mixed leading often happens as a result of merging paragraphs with different settings (deleting end of para)
You have to "clear overrides" as a next step.
The Paragraph ends with a non-character is a larger font size (sorry not sure how to describe it better)
Try placing the curser to the right of the last letter and press delete then enter
That's it! Don't know how I missed it - many thanks.