Looking at the official raw and the volumes (on BW), the French numbering actually seems to be correct. Neither number the individual parts as single chapters. Another aspect in favor of the French approach is that putting the plot and part (+ repeated title) in the chapter title makes them quite lengthy.
As for the report, the issue seems to apply to all languages (and depending on the language, chapters are bumped even further) but looking at the raws again, the chapter is a bit of an outlier name-wise and is exceptionally short, so maybe it is sort of an omake / extra chapter, meaning leaving it as .5 would be fine. Chronologically it seems to be in the right spot. And if the chapters were to be renumbered to follow the French, the decimal point would already be used so they simply numbered it 2.7 to keep the right order.
While adjusting all other uploads to match the French would arguably be more work, I still think it's more accurate, so I (or anyone else interested) could make a list of the necessary chapter number (and title) changes if that's the version that gets decided on.
Regarding the report, I think leaving the chapter as .5 is fine as is. If anything, volume 4 needs fixing because the English TL stuck to treating ch. 9.5 as a full chapter, so their chapter 23 is chapter 22 in the other languages that either didn't include the chapter at all or included it as .5
If we were to renumber chapters anyway, that would resolve the issue as well though.
