Plurality of a group also referenced using we/our/us

ABC is expanding our operations overseas.

This is grammatically correct, but doesn’t have the intended meaning. Our cannot refer to ABC because they disagree in person: ABC is third-person while our is first-person. In that sentence, ABC is transitively expanding “our operations”.

If we’re treating ABC as singular, then it should be:

ABC is expanding its operations overseas.

Treating ABC as plural:

ABC is expanding their operations overseas.

If the intent was to add emphasis to the fact that the speaker is part of ABC:

We at ABC are expanding our operations overseas.

This is a very interesting question. From my (AmE) perspective, it doesn't seem odd at all, and out of curiosity, I scanned through several of our corporate memos and found numerous examples of just this sort of thing.

On the US side, ABC are isn't a viable option for companies or teams like it is in the UK. However, it's fairly common not to refer to the a company/team/etc. as a 3rd-party entity (when you're a part of that entity). It creates a more distancing feel, and typically you would want everyone to feel that they're a part of the entity, not on the outside looking in. So to counter that, rather than using it or its, its common to use we or our.

I think when you combine these competing forces you end up with examples like yours that sound fine to my ears despite, admittedly, seeming to violate grammatical number (and perhaps even a 1st/3rd person crossover)

It is not a transatlantic thing, it is just a poor grammar thing. Putting them in the same sentence should grate. I think the reason the second sentence is less offensive is that the plural and singular are further apart; the sentence break adding a lot of distance. It is still annoyingly wrong, but the distance means the conflict is less obvious.