Single Series menu item has stopped working on one of our sites

Hello. 

I currently have a sermon page set up for a client.  www.richlandhillsbc.com/sermons

Each image on this page links to a Single Series menu item on a hidden menu. This was working fine last week but is no longer working. 

I tried using other SermonSpeaker menu item choices and all of them are working correctly. It is just the Single Series option. 

I know that we need to upgrade and we are going to but we have a lot of clients to get through. 

Any help would be greatly appreciated. 

Please let me know if you need additional information.  

Since it shows an error, it would be interesting what the detailled error message looks like in the server error log.

And did you maybe update your PHP version lately? If so, then what version are you currently using and which version of SermonSpeaker?

We are running sermon speaker version 5.9.9.

Yes, our PHP was recently updated to PHP Version 8.0.0.

I am getting this message: 0 - Cannot access offset of type string on string

Click the link provided below and you will be taken to their sermons page. Click on any Sermon Series image and you will see the issue.

www.richlandhillsbc.com/sermons

Can you enable debug mode in your Joomla to see the full error message? It should also tell you in which file and on which line the error occured. The server error log may also have this information.
I ask that because the SermonSpeaker website is running on PHP 8.1 and SermonSpeaker 5.9.9 and it doesn't look like this error happens here. So I need a bit more details as a starting point

I have turned on the sites debugging. I have attached the error log. 

I don't see an attachment. But you can send it directly at admin@sermonspeaker.net, then it should work for sure.