Often times when a download starts it will get to a certain percentage of completion and them will get stuck.

The reason I say stuck is because it will say downloading from 3 hosts or 4 hosts etc, but speed shows 0 KB/s which I am thinking means it is not downloading at all.

Am I right, if so, why does it show multiple hosts downloading but no progress?

Is there a way I can start or restart the download when it gets in this mode?

Right click on the file on the search results page > search more > get more results.
Also try doing a new search for the file, sometimes that can kickstart a download.