If you use gulp.dest() to update a .php file that is used as an include via require(), require_once() and I belive the include() variants on a system with opcache enabled you're gonna have a bad time.
On linux based systems, gulp.dest() sets the modified time stamp of the output file back to the source file's modified time after writing it. This leaves the mtime of the file unchanged when directly editing an exisiting file via gulp (this is not the case on windows). This is a problem if the .php file written is used as a PHP include on systems with opcache enabled. Opcache will assume the file has not changed and therefore not read the file again. It will instead just assume the result of the include file from the last time it was actually ran.
To work around this add gulp-touch-cmd via npm i gulp-touch-cmd --save or npm i gulp-touch-cmd --save-dev depending on your project, then add const touch = require("gulp-touch-cmd") to your gulp file, and append .pipe(touch()) to your .pipe(gulp.dest()) calls where the file mtime value being updated is important.
Now when you run the compiler the file's mtime will be current and thus opcache will invalidate its previous result.