Thanks for asking.
Please try adding following code in .htaccess file and save the changes:
SetEnv MAGICK_THREAD_LIMIT 1
You can refer following article for more details on editing .htaccess file https://www.shoutmeloud.com/how-to-edit-your-wordpress-htaccess-file.html
I also noticed that you are using an old version of Pro Theme. As of now you are runing Pro Version 1.1.1 and as of today we have version 1.2.7. In that regards I suggest you to update Pro theme as running old version will cause potential issues and security loopholes. You can refer our changelog for more details https://theme.co/changelog/
If you need help in updating theme, I recomend you to refer our theme update guide