This theme is built around Piklist WordPress framework which hasn’t been updated for a while. I wrote about the problem at Piklist official website (support forum) here: https://piklist.com/support/topic/class-piklist_revision-issue/
Author promised to fix the bug with the next update, however it didn’t happen yet. Until it happens you’ll have to do the following:
1) open “your_site.com/wp-content/plugins/piklist/includes/class-piklist-revision.php” for edit
2) go to line #27 which reads the following:
add_action('save_post', array('piklist_revision', 'save_post'), -1, 2);
...and replace with this:
add_action('save_post', array('piklist_revision', 'save_post'), 99, 2);
3) save “class-piklist-revision.php” and re-upload back to the server to “your_site.com/wp-content/plugins/piklist/includes/” folder – if you edit the file on localhost.
The above solution will fix the problem with non-saveable “Page Builder Template” – until Piklist gets officially updated. At the time it happens everything should be working fine.
May apologies for any inconveniences, I wish I could update Piklist by myself!