Impromptu photoshoot plans happen all the time. We (my group and a bunch of others people we met at con) ended up planning a shoot in all of two hours on the last day, and got so many people. If that can happen with a shoot that isn't preplanned, having more than one shoot for a series at a single con that's PLANNED is also possible, and it doesn't always have to be the same people running them. Maybe someone put together another photoshoot completely separate from yours, but they actually told the staff about it, and it ended up being put in the "official" schedule at the front desk. Miscommunication happens, but it doesn't necessarily mean that whoever is responsible for that photoshoot was actively trying to undermine anyone else.
I know that for me, personally, I don't normally attend large 'official' photoshoots for my fandoms because they tend to be alot of sitting around waiting for your character to be called, and then you're up there for five seconds to be photographed and then it's more sitting around for HOURS (in the hetalia fandom especially) while every other character is called. possibly in the hot sun, in a hot cosplay, on uncomfortable ground. So I tend to put together/attend smaller, less official-like side photoshoots where there are less pairing options, sure, but there's also less of the sitting around and more of the having fun.
Is it possible that a side shoot like that ended up 'supplanting' your official shoot by accident? YES.
Can you absolutely guarantee that the people running it were doing it out of spite or because they 'wanted to take your place'? NO.
Personally, all I can say is that maybe you can try again next year, and this time try and make sure that the staff at infodesk with the printed list KNOW that they are two separate photoshoots for the same series, run by two different groups of people?
/end my 2cents
