Was the 325 pure Coservatives and DU? Two abstentions from the group? Deliberate or permitted?
At any given moment, a seat or two is usually unoccupied due to death or resignation. Or maybe somebody is sick and unable to make it to Parliament. Or a seat has changed hands from one party to another in a by-election.
Some Labourites at odds with Corbyn or the party establishment or in serious legal trouble also abstained.