The argument that the functions of the Electoral College are not “official proceedings of Congress” is intriguing. Members of the government and Congress cannot be Electors. The tallying of the Electors’ votes is done before a joint session of House and Senate. They only have a role to play if there is a tie, which obviously was not the case in Jan 2021. “Official function” in common sense language does not necessarily mean the same in law. In federal law, it seems to involve matters with testimony before a judge.
If the judge WANTS a technicality to dump the cases, this might do it. It he doesn’t, he can bend it the other way.
It’s also questionable whether the charged individuals “obstructed” anything. There is no evidence that particular defendants thought about entering the building before the EC tallying was moved pre-emptively to another location. The EC vote took place. Perhaps Congress could be charged with obstructing itself.