Are you using SMUSHIT or something like that that minifies? That was a reported conflict from some of our users months ago. You will need to deactivate it.
Other suggestion: go through the WP debugger or troubleshoot by shutting off all other plugins one by one to rule out conflict.
You should have a backup to restore to if anything goes awry. P.S. It is suggested as WP best practices to Update MySQL to 5.6 or higher
https://wordpress.org/about/requirements/