Add the temporary Javascript line window.alert('Turn on Performance Recording') just prior to Engine Instancing line.
Load the scene, turn on performance profiling, & click ok to the temporary alert.
Do anything that might call code in babylon.js not yet encountered.
Stop recording, and save the data as a file.
On this page:
Select the branch to build the config against. Be sure to change to that branch in repo
Select File with 'Browse' button below, and pick the file saved from above.
Make any changes of name to babylon file names & directory..
Click Generate. Tip: change Firefox Option for Downloads to Always ask me where to save files to avoid having to move config with custom entries to Gulp Directory.
Copy the 'custom.cofig.json' file generated in Downloads directory to the Gulp directory.
Run: 'Gulp build-custom' then test with scene. Tip: test with the generated max version.
If need stuff did not get recorded in performance file, then select file(s) & click Generate again.