Image styles are not beeing generated I have a problem where Drupal tries to access the files in the "styles/stylename" directory, but they are not there since they aren't beeing generated. I allready tried changing the theme for a while (image style (imagecache) images are not being created) and also tried creating the style folder, changing permission and editing the .htacces file (https://www.drupal.org/forum/support/post-installation/2015-06-16/image-styles-not-generating#comment-11859066). I also tried a few other things, nothing seems to work.  
Maybe usefull information: the images are created in a directory based on the month and year. 
 for example "sites/default/files/2019-07/filename.png" 

edit:
When accessing the url of the image style it returns:


  Error: Class 'lsolesen\pel\PelJpeg' not found in Drupal\file_mdm_exif\Plugin\FileMetadata\Exif->getFile() (line 108 of modules/file_mdm/file_mdm_exif/src/Plugin/FileMetadata/Exif.php).
      Drupal\file_mdm_exif\Plugin\FileMetadata\Exif->getFile() (Line: 127)
      Drupal\file_mdm_exif\Plugin\FileMetadata\Exif->doGetMetadataFromFile() (Line: 280)
      Drupal\file_mdm\Plugin\FileMetadata\FileMetadataPluginBase->loadMetadataFromFile() (Line: 377)
      Drupal\file_mdm\Plugin\FileMetadata\FileMetadataPluginBase->getMetadata('Orientation') (Line: 183)
      Drupal\file_mdm\FileMetadata->getMetadata('exif', 'Orientation') (Line: 39)
      Drupal\image_effects\Plugin\ImageToolkit\Operation\gd\AutoOrient->execute(Array) (Line: 172)
      Drupal\Core\ImageToolkit\ImageToolkitOperationBase->apply(Array) (Line: 124)
      Drupal\Core\ImageToolkit\ImageToolkitBase->apply('auto_orient', Array) (Line: 143)
      Drupal\Core\Image\Image->apply('auto_orient') (Line: 138)
      Drupal\image_effects\Plugin\ImageEffect\AutoOrientImageEffect->applyEffect(Object) (Line: 302)
      Drupal\image\Entity\ImageStyle->createDerivative('public://2018-05/02_1.jpg', 'public://styles/project_gallery_image/public/2018-05/02_1.jpg') (Line: 161)
      Drupal\image\Controller\ImageStyleDownloadController->deliver(Object, 'public', Object)
      call_user_func_array(Array, Array) (Line: 123)
      Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber{closure}() (Line: 582)
      Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 124)
      Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) (Line: 97)
      Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber{closure}() (Line: 151)
      Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 68)
      Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 57)
      Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 47)
      Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 99)
      Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 78)
      Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 47)
      Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 52)
      Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
      Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 693)
      Drupal\Core\DrupalKernel->handle(Object) (Line: 19)
Try to installed missed library by the following comment on the root of your drupal website :  

composer require drupal/image_effects:^2