If I add a conversation or post and someone replies, when I try to view it I get "http 500" server error.

I inherited an UNA server and out of all 3 that we run, this one was an existing server which we upgraded from 10.x to 12.1.0. The company I work for had a site built over a year ago and we wanted start using it so I performed the upgrade including all modules as we incremented versions. Yesterday when testing the server on 12.0.1, I noticed that when I created a new conversation or post if any of the users replied, as soon as I went to click to view the thread, I would get an http 500 error. The unusual thing about this is that if I go to the user's profile I can see their comment but when I try to view the entire thread, I get that error. 

Thinking that this was an issue with 12.0.1 I upgrade to 12.1.0 and still saw the same issue. I then removed and reinstalled the conversations and timeline modules thinking that this was the cause and made sure that everything matched the settings on the other 2 servers we run. I even thought that changing PHP from 7.4 to 8.x would resolve this but no such luck. 

My only hint that something is wrong is in the error log below and prior to upgrading to 12.1.0, I got an error about modified files for author_link.html, author.html, form.css and unit_meta_item.html being modified and so I had to force the upgrade. I did make a backup of the files prior to upgrading but they appear to be identical to the files placed during the upgrade. 

Does anyone have any ideas where to look to resolve this? Thanks 🙏