Hi Cade
The render command outputs one file for each tiddler. In this case, the files are all called “ChangeLog.json”, so they overwrite one another.
The fix is to use a filter expression for the output filename, and generate a filename from the title:
tiddlywiki “Data Mart User Manual” --render “[field:change.from[7.0SU2 (7.0.Local)]][field:change.to[9.0 (9.0.Local)]]” “[encodeuricomponent[]addsuffix[.json]]” text/plain “$:/core/templates/json-tiddler”
Best wishes
Jeremy