Warning: Illegal string offset

Hello,
I am new to wordpress and do not have much experience. On the homepage, https://okemomountainschool.org/, when you click on each specific news posts, I am getting this message ‘Warning: Illegal string offset ‘custom_option’ in /home/okemomts/public_html/wp-content/themes/wpuniversity/single.php on line 12′

I am assuming it has to do with the wordpress university theme I am currently using, but I have done everything I can think of to try and fix it, to no avail.
Please help! Thank you.