Premiere Pro CC 2022 exports but will not do a simple render

I am having a rendering problem.  I have been working on a 14 minute video for about a month, using Premiere Pro 2020.  During that time I have rendered it (Render whole work area) many times. Two days ago I took a break.  I came back today and the first thing I tried to do was render. It went for a short time, stopped (not slowed) and this error came up:  Video Preview Error/Error Compiling Movie/ Unknown error.

I closed the project, opened a saved version from 2 weeks ago and tried to render that.  Same error.

I tried restarting the computer, rendering with software only, checking the room in my cache disc, tried to cache to another hard drive, etc.  Nothing helped.  

I updated to the latest version, PPro2022, assuming that would cure everything.  No help.

I then opened a totally different project in PPro 2022 and it rendered fine.

I then took a small piece (50 seconds, 4 clips) of the current project (the one I am having trouble with) and exported it as H.264.  It exported perfectly.  I then tried to render that same small piece, and got the error mentioned above.  The current project is in .mp4.

Judging from the size of clips in the tests I have done, and how far the blue strip goes in the render window before stopping, I think the render is going as far as the junction between the first and second clip in the work area, and stopping there.

I have tried troubleshooting procedures recommended on Google, and in Adobe without any luck.

It appears that the issue is only with this one project, and only recently.  I suppose I can just push ahead

and finally export, but it sure is useful to be able to have a rendered version before exporting it. Can someone suggest a way to approach this?