Calling on the experts here!

As a 0.94 ACMM, I probably qualify as a seasoned AC flyer. But something happended a few days ago that I had (fortunately) never experienced...

Long story short (well not so short!):

Flying out at 11am out of YQB to YYZ with onward connections to US and then international. Checked in online at -24h. Get my 3 BPs. Checked flight status at 6 am on day of departure, all is still fine. Go for a short run, pack my stuff, and as usual check flight status before heading to the irport (YQB). Surprise, first flight (out of YQB) cancelled. Things happen (would still have appreciated an email, call or text from AC, but none). Check flight schedule to YYZ, still possible to get on the earlier flight, call SE line, and after a first 'impossible sir', I insist and get a seat on the earlier flight and rush to the airport. I get all 3 BPs at YQB and get on the flight to YYZ. At YYZ, go through a few BP checks as usual and get to the TB MLL where my BP is scanned, as usual.

So far, nothing special, right!? Then I get to the gate, and surprise, when the GA scans the BP. I hear an usual sound and see the GA starting to punch his keyboard frantically! I start worrying, and after a few seconds, he hands me a brand new BP. I check the BP and realize that I had lost the single seat that I had booked a couple of months ago (J on an E175) . Ask him what was the deal. He does not respond, I insist. He tells me that I had been offloaded... was a bit upset, especially when I found that the seat was a window and the IFE out of order. But that's a detail. In the end I got to my final destination, and that's what really matters, right!?

Other things happened during this trip, but nothing out of the usual. But this offloading thing never happened to me before, does anybobody have a clue of what could have happened, I am curious and would like to avoid it in the future...

Thanks for reading...

R&F