Error - Undefied offset ... seo_url.php

I am using OpenCart 3.0.3.2
I am seeing the following error in the error log:

PHP Notice: Undefined offset: 0 in /home/servc674/storage/modification/catalog/controller/startup/seo_url.php on line 29

I have been using the site several months with no error like this, but only started seeing it recently.

I this a serious error I should fix?
Can anyone suggest a way to fix or troubleshoot this error?

Let me know if I need to provide any more details.

Thank you.

Error comes from modified file and might be related to one of the modifications. Find out which modification makes changes to this file and contact its developer.

It could also be your host has upgraded the PHP version, and it's now showing a notice that it kept quiet before.

I looked at the file at line 29 and it references one of my extensions.
I will contact their support to see if they can help.
Thank you all for the feedback.