How to unstick an area that will not render?

i have been using PE heavily since 2011 and have made truckloads of good projects.  I am now doing a fairly complex project that involves putting MPEGs on to PE of previous PE work.  I have a 70 second section that has two MPEG running simultaneously that will not render.  So, when I play the PE it looks shaky, especially the titles.  However, the MPEG of this work in progress is okay.

        I have played with the sliders, but the unrendering seems to say, "all or nothing."  I have other areas of MPEG on different tracks simultaneously that work ok.

        Though, since more is to be done, I would like the PE version not to be shaky.  Hence, how do I unstick an area that does not render?

Thanking your reply !!