It's all in the title. The php files that do not have the closing php tag ( ?> ) are not displayed in Keppler. This is a normal use of php in frameworks like Laravel for example.
Just for information, I use Keppler with my students a lot for PHP and Laravel projects and I'd never had this issue (using last version of Keppler and node 12.19.0 and npm 6.14.8).
It's all in the title. The php files that do not have the closing php tag ( ?> ) are not displayed in Keppler. This is a normal use of php in frameworks like Laravel for example.