bbPress with attachments plugin not working (Fatal Error)

Hi again,

We are running a site with bbPress (https://wordpress.org/plugins/bbpress/) and GD bbPress Attachments (https://wordpress.org/plugins/gd-bbpress-attachments/) and we get a Fatal Error when trying to attach a file to a forum topic or to a reply.

Error message:
Fatal error: Uncaught Error: Call to undefined function file_is_displayable_image() in /public_html/wp-content/plugins/ilab-media-tools/classes/tools/s3/ilab-media-s3-tool.php:494 Stack trace: #0 /public_html/wp-includes/class-wp-hook.php(300): ILabMediaS3Tool->handleUpload(Array) #1 /public_html/wp-includes/plugin.php(203): WP_Hook->apply_filters(Array, Array) #2 /public_html/wp-admin/includes/file.php(420): apply_filters('wp_handle_uploa...', Array, 'upload') #3 /public_html/wp-admin/includes/file.php(450): _wp_handle_upload(Array, Array, NULL, 'wp_handle_uploa...') #4 /public_html/wp-content/plugins/gd-bbpress-attachments/code/attachments/front.php(116): wp_handle_upload(Array, Array) #5 /public_html/wp-includes/class-wp-hook.php(300): gdbbAtt_Front->save_reply(4740, 3617, 3614, 0, 1) #6 /public_html/wp-includes/class-wp-hook.php( in /public_html/wp-content/plugins/ilab-media-tools/classes/tools/s3/ilab-media-s3-tool.php on line 494

We tried with with jpg, png and pdf files (separately).
Any chance you can help out to solve this issue?

Thanks!