@azraei97 It's actually just Chapter "EX", so while it's placed at the end of the volume it's not numbered and so we opted to use the magazine order instead (it's still labeled as the correct volume, which is what actually matters here). Our translator asked on the mangadex discord about this issue but received no response whatsoever so we assumed that the staff doesn't care.
Also the staff didn't fix chapter 10 (A Date with Shion) yet which is the previous Chapter "EX", which unlike the current case, was actually put 1 volume further in the volume version than it was in the magazine version, i.e. it's in Volume 3. So right now we have two "Chapter 13" instead.
This current predicament stems from the fact that magazine chapter 10 and magazine chapter 31 had been made into EX chapters in the volume version making the two versions diverge in terms of chapter numbering and in addition while anejlek (mostly) uses the volume version raws, Desu Vult and we (Tempest) use the magazine version raws.