Sparking white screen of death

Today, I had a dead site. A White Screen of Death. Totally blank. No HTML loaded for the home page or any other page URL.
I disabled all plugins, but that did not help.

The error log said:
“PHP Fatal error: Uncaught Error: Call to undefined function of_get_option() in …/wp-content/themes/sparkling-child/header.php:27”
The offending line (in header.php) was
I removed that line, but that did not solve the problem.
My other sites on the same host were OK, so it not likely to be a PHP or hosting error.
I activated the Parent Sparkling Theme, and the site came back up. I then re-activated the Child Theme and the site remains up and running! All Good, except that I have not been to identify the core issue.

Sparkling Theme is at Version 2.4.8 but I have been running that version since January 2021.
WordPress is 5.5.7 and PHP is 7.2.34

I cannot say for sure it was a Sparkling issue, but it seems that is where the snag may have been.
I’d be grateful to hear any thoughts or guidance from you.

Thanks

Hi there

Please send your admin details in a private message and I will check your problem

Hi, I am sorry but the client (I run their site) is unwilling to allow external access to the CMS. For privacy reasons.

Is perhaps you can tell me the specific information you need, I can see what I can provide

Thanks for the support

Hi

Usually such thing is not happening, that’s why it needs to be investigated, first of all, make sure you are using latest version of the theme, you are not using any modified version of the theme,