GPU Render Error Unable to process frame. Writing with exporter: H.264

It's video content that I downloaded from the web and I'm compositing together, so I have no idea about the source, but from the quality I suspect it's mostly shot with cellphones.   It's not for publication so I'm not worried about copyright -  the whole purpose of this exercise was to test out my new PC with a fresh installation of Premiere Pro.   The total sequence is 18 minutes long and is comprised of about a dozen clips.  There are literally no effects; no scaling, no color or contrast or sharpening or LUTs or stretching or scaling or anything.   I just took some clips, edited out the boring parts, butted them next to each other with the default transition and overlaid it with an audio track.  

The crash is happening where the first two clips butt together.  I know that butting two clips together is not the preferred way to do it as opposed to nesting them or overlapping them on separate video tracks but I've never had it produce a crash before. 

N.B.  During the last hour I've started a whole new project where I'm trying to recreate the same sequence manually, editing out the boring parts, and butting them together on the same video track with the default transition; every time I add or edit a new clip I re-render it.   So far no crashes even though I've already added the clips that crashed in the original.   Since I'm doing this slowly and meticulously I have many more hours of work ahead of me, but even if I get to the end with no crashes this is still unacceptable to have something that crashes randomly with no clear reason or confidence that it won't happen in my next project.