Lagging prior to fully caching, yes, but have never seen the screen go black. It's unclear whether this is the issue cited above. Thoughts...
1. Drag the preview screen smaller.
2. Break up the project into parts, export each, then import and merge the intermediate exports for final export.
3. Create a proxy, to lessen the work that the program has to do...
Run the podcast through a converter (or use VP) to reduce it to very low resolution. Then load that file, make your edits, and Save Project Files AS, giving it a unique # or name so as not to overwrite prior saves.
When ready for the final export, prior to starting VP, rename the low-res file that was used for the edits.
Double-click the VPJ saved project file, which will start VP. Since it can't find the renamed file, it will prompt to resolve. Point it to the original higher-res file. Export.