Comment by Philip-J-Fry

I also saw a similar thing. I also naively pointed at "cosmic rays". It wasn't until someone found the actual bug that I realised how unlikely that was.

The actual bug was unsafe code somewhere else in the application corrupting the memory. The application worked fine, but the log message strings were being slightly corrupted. Just a random letter here and there being something it shouldn't be.

The question really should have been, if this was truly cosmic interference, why only this service and why was the problem appearing more than once over multiple versions of the application?

Cosmic rays are a great excuse to problems you don't yet understand. But the reality of them is extremely rare and it's like 99% a memory corruption bug caused by application code.