I haven't found yet what is causing the warning, so I can't answer that one.

I am not totally sure what the bad effects of a deep recursion are: someone must think it is bad or there wouldn't be a warning. I wouldn't remove the battery from my smoke alarm at home, and turning off warnings feels a bit like that, but am I being too cautious?.

As to the data, the entry is quite large and has a deepish tagging structure which might be the problem, though the parser works on larger more complicated entries so I am not conviced about this possible explanation

I typically do following steps in such situation:

1. Write the simplest code to product the same effect (warning in your case). You would exactly know which part of the code warns you.

2. Write the simplest data to product the same effect. Perhaps one element with deepish descendants could proof your idea.

In addition (and usually before doing what you suggested) I would google for the message to see if it's maybe a known bug, and the problem might perhaps be solved by simply installing a newer version.  Even if this doesn't lead to an immediate solution, you'll often find related discussion which gives new ideas what to try.

I'm not saying this is necessarily the case here, just advocating the heuristic in general... (seems obvious, but I still often find it not being heeded)