The wp-config.php generated for WP Engine installs replaces the standard WordPress marker comment // with custom wording (# That's It. pencils down). WP-CLI's wp config set matches the standard comment as a literal string for its default placement anchor, so the substitution causes the command to fail on every install with "Unable to locate placement anchor".

Please restore the standard marker — or, if the custom wording is deliberate, emit it in addition to the standard comment. Either restores compatibility with wp config set and the wider tooling ecosystem built on wp-cli/wp-config-transformer, with no functional change to the file.

If amending the template isn't possible, please confirm the officially supported method for adding constants to wp-config.php at scale across an account's installs.