Unfortunately, there is an issue with Handlebars that stops it from being used with ncc.

Until this is addressed the node-modules folder needs to be committed to the repo containing the production dependencies for use at runtime.

There error is

Processing template
Error: Invalid left-hand side in assignment
##[debug]Node Action run completed with exit code 1
##[debug]Finishing: Run /./

This has been logged with Handlebars as #375