Debugging build and push

[subtledigital]

Having issues building and pushing a theme.

Stencil start works perfectly with no errors in console but when trying to build or push I get the following quiet error

Validating theme...
SCSS Parsing Started...
Template Parsing Started...
Language Files Parsing Started...
Building Theme Schema File...
Schema Translations Parsing Started...
Theme task Started...
ok -- Theme Schema Building Finished
ok -- Schema Translations Parsing Finished
worker initialization failed
ok -- Language Files Parsing Finished
ok -- SCSS Parsing Finished
ok -- Template Parsing Finished

Any suggestions on how to debug the above?