As it's a couple of months after I posted the question, and https://blog.stackoverflow.com/2011/07/its-ok-to-ask-and-answer-your-own-questions/ I guess I should state what the outcome was...
I couldn't find rhyme or reason for the issue other than removing the comments resolved the issue. Now that this has in effect been included in our rules to follow, we haven't come across this issue since.