@brightsite $spacer is a Bootsrap 4 variable. It’s like somehow your style files got overwritten from a newer version of Sage. When you compare your current files to your repository (either the current state of your repo or previous commits), do you see different versions of _grid.scss or _wp-classes.scss?
You have a few options:
- Fix everything for Bootstrap 3 (revert all SCSS files that are calling BS4 variables or mixins to a copy from a previous version of Sage and run
bower install). - Fix everything for Bootstrap 4 (this is potentially more challenging and risky depending on your theme). See here: Sage 8 legacy sites and Bootstrap 4 stable version
- Go with the Bootstrap CSS file you’re including in your head template. (Which would require removing the imports for files that are calling Bootstrap SASS variables or mixins, or modifying those files so they don’t use those things.)