I have submitted
PR 2912 to fix this issue. When accepted, it will show up in the
devel branch. In the meantime, you can fix this yourself:
1. Open the leoPyRef outline using the File/Open Specific Leo File menu item.
2. Do a search for the string headline_str = '##' + headline
3. Add a space after the ## so that the string now reads
headline_str = '## ' + headline
4. Save the outline and restart Leo.
This fix will work until the next time you update to a newer version of Leo. The newer version should include the change. This all assumes that you have been using the viewrendered3 plugin.